Flat Earthers are stupid. The theory of a flat Earth is easily disproven. If the Earth were flat, everyone in every place on Earth would look up at night, and see the same stars / constellations, overhead...from a slightly different angle, but the same constellations. Everyone, everywhere-Canada, USA, Australia, South Africa, etc-would see The Big Dipper, and The Small Dipper, for example. In fact, people in The USA see different constellations than do the people in Australia...because the Earth is a globe with northern, and southern, hemispheres. People in The USA see The Big Dipper. People in Australia NEVER see The Big Dipper, but do see The Southern Cross....which people in the USA never see. There is NO way this fact can be disputed, or explained, by The Flat Earthers.
I've been a Prime member for years. It is worthwhile.
These days, I only take what I can carry on with me. I check nothing. If I were you, I would take the 14-24mm lens, the 70-200mm lens, and the D500 camera, and the bean bag. I'd leave the rest at home.
I dabbled in pinhole photography years ago. I tried it with a cardboard box, and with a Lubitel camera. It was interesting, but I prefer sharper images than a pinhole can provide, so I went back to lenses.
If displayed in public-on a street, for example-the work is fair game, and photographable. If displayed in a more private place-a mall, a store parking lot, etc-limits can be placed on your ability to photograph items / people. A park, or fairgrounds, or a street closed off by barriers, might be considered private property, rather than public property, since it belongs to a city, or a county, which-after all-is a corporation with some private status as well as public status. Whether you actually have to, or not, it is best to respect the wishes of artists, fair goers, etc, and not photograph what they don't want photographed. If you want to push it, and photograph anyway, stand off the property-across the street, on a sidewalk-and use a telephoto lens to photograph subjects from that distance.
An 85mm lens would be good for portraits. Nikon has one...the AF-S 85mm F/1.8G. It is an FX lens, which will work on your DX camera, and lists at $479.95. Go for it.
Both are basically good cameras. The D750 has a few more bells & whistles, but has also had more recalls lately.
Learn to use your tongue, well, and women won't care about the size of your penis. Study The Kama Sutra Of Vatsyayana.
Are the accessories-battery, charger, etc-from Cameta all Nikon brand items? They may not be. If so, that can be troublesome. I once used a non-Nikon battery in a Nikon camera, and it burned out both the battery, and the camera, neither of which worked after that. The battery was a Vivitar brand, allegedly designed to fit my Nikon camera, but it killed my camera. I tend to only use Nikon brand accessories these days, so I won't buy cameras from sites which include off brand accessories. All of the refurbished gear I've bought from nikonusa.com is still working, years after purchasing it.
The Nikon D5300 is a good camera, but lacks a built in focus motor. If you want an interchangeable lens camera, consider the Nikon D7200 which has a built in focus motor, so it can auto focus with older lenses which lack focus motors (non AFS lenses).
The Nikon P900 has a longer all in one superzoom lens (83X), but it lacks 4K, and has only 16MP. the Nikon B700 has a bit less zoom, but still a lot (60X), and has 20MP, and has 4K capability.
If you work for strangers free, it must be because your work is worthless. That is what most people will think. Do your own photography, and charge for it. If you want to shoot for free do so only for close friends / relatives for whom the shoot will be your wedding gift. Their friends, etc, who see your great photos (if they are great), and will be willing to pay you a reasonable sum to do their weddings, babies, etc.
Years ago, I checked luggage. Every time, something was lost, or stolen, or damaged. I finally stopped checking luggage. Now I only take a carry-on bag, which stays in my lap, or hand, or under the seat in front of me, or in the overhead compartment.
The Nikon B700 is probably your best choice. The Nikon P900 has a longer lens (83X vs the B700's 60X), but it lacks the 4K capability which the B700 has. The P900 also has only 16MP, while the B700 has 20MP. The B700 gives you more capability / features for $250.00 less than the P900 costs. Other superzooms by Fuji, Sony, etc, lack the B700's 60X zoom, and / or it's RAW capability, and/or it's 4K capability, etc. My girlfriend is a Nikon B700 fan.