I use this "Swiss Army card reader" for my Android phone and tablet. It can read or write a SD or microSD card to a USB or microUSB port. It's only $7 and has been very handy. I keep one in my camera bag. Similar devices for iPhone/iPad are available.
https://www.amazon.com/Vanja-Reader-Adapter-Portable-Memory/dp/B00W02VHM6/ref=sr_1_3?s=electronics&ie=UTF8&qid=1513011965&sr=1-3&keywords=Vanja+SD%2FMicro+SD+Card+Reader

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My first DSLR was a Nikon D40 in 2007. After six years and over 35,000 clicks, I gave it to my younger brother. He uses it regularly, although not as much as I did. It still works as well as new. My Grandson is using my (new in 2011) D5100 and it still works as well as new.

If not for GAS (and newer features) I could still be using them.

For over fifty years I've heard the claim "they make them to wear out in a couple of years so you have to buy a new one" about almost every product. "They don't make them like they used too" is mostly bunk from those of us looking back through rose colored glasses with selective memory.

I do the same and add "REWARD" in large letters. If someone found and returned my D7200 I'd gladly pay a $100 reward.
I haven't lost a camera yet, but I lose a cane at least once a year. I put it aside to take a few photos and don't notice I'm without it for a while. Perhaps I should use an over-the-shoulder strap on the cane too.

Many who have not used a diffuser or bounce are astonished at the difference between the on camera flash and an accessory flash with a diffuser.

I've used a flash diffuser for over 30 years. Now I often use a homemade diffuser (thanks Ken Rockwell) on my Nikon SB-400 flash.

When my niece was married recently I saw the "Professional photographer" shooting only one shot of poses that I thought most important. I told my brother and he went to the photographer and INSISTED that many more be taken. It sounds as if this guy who called himself a photographer is typical of many these days.

I did Wedding photography for about ten years (in the seventies and eighties) and I took it seriously. I was always aware of how important an event this was for those involved and I always worried about doing everything well.

Wedding photograph was so stressful for me that I gave it up after about ten years. Nowadays I'd sooner shoot myself (with a .38) than shoot a wedding.

I have a V600. I've scanned thousands of slides and I'm pleased with the results (and the price). I recommend the Epson V600.

When I was young I often made the same mistakes over and over.
As I matured I began to learn from my mistakes, and didn't repeat many mistakes.

Now that I'm older and wiser, I'm (usually) able to learn from a mistake made by someone else.
That has often been of great assistance in life as well as photography.

YMMV

Like many others here, I use the Epson V600 for scanning slides. IIRC it was about $300. That was about ten years ago, so I'm sure there's a newer model.The results exceeded my expectations.

The only issues for me were:
(1) How much dust finds its way to my old slides even though they were stored properly. Cleaning can be tedious, often taking more than one attempt.
(2) How much time scanning takes - I have many thousand slides. While slides are scanning I use a small light box and loupe to preview more slides and choose which to scan. Background music helps.

To me the Epson V600 was a lot of bang for the buck and I'm retired with lots of free time.

YMMV

Here's a 40 year-old Ektachrome that my wife took (after I set the camera and handed it to her.) Some dust got past my first attempt to clean.

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On vacation about 30 years ago a shoulder strap fitting failed and my Canon A-1 camera and 70-210mm zoom lens fell to the concrete. When I picked it up I found two pieces; my camera had the lens mount still attached but the rest of the lens was a separate piece.

When I got home I went to the repair shop. I put the pieces on the counter and asked "What do you think Allen?" There was a long silence, then he removed his hat and held it over his heart.

I hope you have a better result.

Always in my bag:
. Nikon D7200
. Nikon DX 18-200mm VR II
. Nikon DX 10-24mm.
. Nikon DX 35mm f/1.8

If not walking far from the car I'll often leave the bag and carry just one camera and lens.
Otherwise it's one camera and those three lenses.

often carried, but not everyday.
. Nikon D7000 (backup body)
. Nikon AF 300mm f/4, with TC
. Rokinon 8 mm fisheye

Mac vs Windows is like Canon vs Nikon. Almost everyone has an opinion. They both will work for you.
If you have computer experts in your family who can and will help you, then get what they recommend

1920 by 1080 is the absolute minimum now. I recommend buying the largest, highest quality monitor possible. Better yet two of them. If you do buy a laptop you can bring it to your desk and easily connect your large monitor(s).

Desktop computers are less expensive than equivalent laptops, and are cheaper to repair and upgrade. I'd only recommend a laptop if you are COMPLETELY SURE that you need to take it with you when you leave home. Many people end up leaving the laptop at home on a desk and rarely or never taking it anywhere.

Warning: you can contract computer GAS too. I spent most of my budget a few years ago (what remained after camera GAS) on a high end desktop, a bunch of hard drives, and two good 27" 1920 x 1080 monitors. I'm now thinking about getting larger, 4K (higher resolution) monitors. I bought a cheap laptop but rarely do any photo work on it beyond looking briefly, and making backups - one copy to the laptop's HD and another copy to the slim portable external HD.

I'm pleased with the Nikon DX 35mm f /1.8 lens that I've used for a few years on my D5100 and D7000, and now on my D7200. It is sharp and the two stops more allow me to use higher shutter speed and/or lower ISO. I like the Bokeh.

All other things being equal, a fixed focal length lens will be sharper than a zoom lens.

I agree with fourlocks about weight and shoulder strap. I carry a D7000 or D7200 with a battery grip and Nikon 18-200mm lens that weights 59 oz. One day I grabbed my wife's Nikon D5100 with 18-55mm lens (28 oz) and was amazed by how light it felt, even on a short walk.
The D3400 with the kit lens weights about 23 oz, with the Sigma 18-250mm lens about 33 oz. Unless you have specific photo goals that include that powerful telephoto I suggest getting the D3400 (or as many here suggest, D3300) with the 18-55mm "kit lens". If you later find a need for a more powerful telephoto lens and buy the Sigma 18-250mm (or Nikon 18-200 or 18-300mm) you'll have only spent about $50 more.

Recently I helped an in-law with her new D3400 (with 18-55mm lens). I was impressed with its capabilities and low weight. In a discussion with family members, some who've been photographers longer than I have (50 years), we agreed that "back in the day" hearing about the features of a modern entry level DSLR would seem like science fiction.

Grandchildren are responsible for a lot of camera purchases. Whatever choice you make, I think you'll be happy with your new camera and the results.

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I bought a refurbished D7200 direct from Nikon when they had a $100 off sale at the end of June. It had 195 clicks and looked like new. Previously I'd purchased an SLR and two lenses refurbished and they also looked like new and worked perfectly.

I more than doubled the click count in the first two days testing it in all modes with all my lenses. I'm completely satisfied with it and now have over 3,000. The AF seems faster than my D7000 and the larger buffer is great. (On the D7000 I sometimes had to shoot JPG instead of RAW just to keep from filling the buffer.)

I think you'll like the D7200 just as much.

After using my D7000 for a couple years I considered battery grip. I wasn't sure that I'd like it so I bought an inexpensive one - Neewer. It fit and worked well. I have large hands and I love the controls for portrait mode. I don't think I ever needed the extra battery - up to 750 shots on the first battery - but it was reassuring to have two.

When I bought a D7200 in July I ordered a Neewer for it. This battery grip did not fit flush to the bottom of the camera body and never felt secure so I returned it and bought the Vello battery grip. It fit and works well.

I keep the battery grips on the cameras almost all the time now. I also usually have an Arca Quick Release L bracket mounted since I use portrait mode more often.

The weight is a minor issue, especially if I'm carrying both cameras (and a tripod and another lens) and walking far.