By the way, I purchase those Lenovo laptops off of eBay. There's an i7 P50 on there now for ~$550.
I don't know that you're interested at all in a larger printer, but Canon regularly runs deals which will allow you to get a Pixma Pro-100 (13x19) 8 color printer for around $150.
I suspect the least expensive path to the highest spec machine is a custom built desktop. However, like you, I like laptops. As a mechanical engineer, I've run CAD stations for a couple of decades. In 2012, when I wanted to purchase a laptop, I had been having such good luck with my Lenovo W520 at work that I purchased one for myself. Here's my experience: Engineering laptops are designed to run 3D graphics all day, every day. The W520 my daughter uses (from 2011 with an i7 processor, dedicated graphics card and SSD I installed with 16GB RAM expandable to 32) runs Photoshop, AutoDESK Maya, the full Adobe Creative Cloud, etc. quite well. Last year I passed my similarly spec'd W520 to a relative and upgraded to a P51. The P51 also has an i7 processor, 32GB ram (expandable to 64GB), Nvidia graphics card (4GB) and three hard drive bays. I'm familiar with and have had the best luck with Lenovo, but Dell and others make engineering workstations as well. In the Lenovo line there's the W520, W530, W540, W541, P50, P51, P52, etc. Always get the i7 model.
For me it would come down to this: if you have money for a lens or two and value auto-focus, the 810 is the better all around camera. If you have very little for lenses and are open to manual focus, then the focus peaking and ability to adapt most lenses ever made to the a7r may be more advantageous.
I've got an a9ii, so similar generation. I keep the rear display turned off (it's one of the toggle options). When I put the camera to my eye the EVF turns on and it's all good. If I review an image or bring up a menu the rear display will turn on and show the info and then turn back off (if I'm not looking through the viewfinder, of course).
I'm not a Facebook expert, nor am I a photo critic, but I suspect Facebook's algorithm had something to do with it. It may have been that it really struck a cord with an early viewer who commented. The comment got it in front of more people (due to the algorithm) and the momentum continued to build. I actually like both pics, although I like the second better.
Bird in flight isn't my specialty, but on my a9ii with the 200-600 (and the 100-400) I keep it in AF-C, single or continuous (depending on what I'm trying to get), medium flexible spot with tracking on the AF-on button and medium flexible spot without tracking on the AEL button. I'm shooting in manual with auto-iso and setting my shutter speed and aperture myself (s mode would work also). For shutter speeds I go between 1/250 or so when light is low and the bird isn't moving up to 1/1200 or more if they're flying around.
Mark Galer and Mark Smith both have extensive setup videos for bird in flight on the Sony's.
I think the Sony version will only open Sony RAW files and non raw files. I don't believe it will open any other manufacturer's RAW files.
KEH is very easy to deal with and their rating system is good (as in items are typically in better condition than you'd expect). If you want to sell or trade to them, you'll almost always get more if you sell it yourself, but they make it very easy to sell to them.
I was blown away by Maymont. If you've got time, Yorktown, Jamestown and Williamsburg are awesome (via the Colonial Parkway). There are also several very cool plantations along the James River.
I'd clean the contacts on the adapter and lenses first.
As has been mentioned, covering 24-1440mm equivalent focal length with a dslr isn't going to come cheap (and practically, 1200mm is about as far as you can expect to get with a 600mm lens and 2x teleconverter). What I recommend is posting the types of things you like to shoot and let people help guide you to sensor size/focal length combinations which work well for those subjects. Each manufacturer will have a variety of cameras and lenses which will likely work, but it all starts with what you want to shoot.
I do want to add, while your B700 has a huge focal length range, the sensor is very small. Given this, you're best results are probably limited to situations where there is quite a bit of light. Depending on what interchangeable lens camera and lenses you get, you will get significantly better autofocus and low light performance.
I like engineering laptops which are designed to run 3d cad. Personally I use Lenovos, but Dells or others can work as well. Both I and my daughter used W520 models with an i7 processor, dedicated graphics card and an SSD (which I installed) and upgraded ram (this model will take 32gb). She uses the full creative cloud and the computer still does fine. I recently upgraded mine to a P51 with current hardware and it flies.