New hobby photographer here.

I need a camera body to pair with a (yet unpurchased) lens for digiscoping with my Swarovski ATX 85-To be used mostly for shooting wildlife

I would also like to get a lens for the recommended body to shoot landscapes

hopefully keeping the price for the body less than $1500 (less than $1200 ideally, but if it is a buy once cry once thing I am good with that)

I already have a tripod/etc

These are interesting times. Canon has the 5DSR listed for $11xx in the refurb store, but they're OOS right now. As the transition to mirrorless happens, I think there will be more deals like that to be had.

At the same time, you really need to choose a mount system and lens, then go with the body afterward. I'm in a strange place right now Canon wise, as they've gone to a new mount.

Swarovski makes a several lenses that mount to different bodys/sensor sizes and then interface directly with the scope.

I don't know a thing about the trend toward mirrorless? Is that a good thing?

I am a super novice, so explaining to me like I'm an 8yr old would help

Link to Swarovski lenses

If you're shooting tele you want a crop sensor and a long lens.

I'm a Nikon guy, so I suggest a D500 body and either the Tamron 150-600 or Nikon 200-500 zooms.

The Tamron gets you a bit more reach but the Nikon beats it for sharpness.  I had a G1 Tamron which I dumped for the Nikon; I like the Nikon much better.  The Tamron G2 version supposedly corrects some of the limitations of the G1 version.

For landscapes you're going to want a full-frame body and a wide lens.  I use the Tokina 11-20 on my D500 and it serves my landscape purposes.

D500/Tamron 150-600
Big Buck by FredMan, on Flickr

D500/Nikon 200-500
Hover by FredMan, on Flickr

D500/Tokina 11-20
Storm Beams by FredMan, on Flickr

And the older Tokina 11-16 with the D500
Hamakua Road That Time Forgot by FredMan, on Flickr

I have the tele lens (swarovski ATX 85.  effectively a 2600mm lens)

Swarovski makes either lens for either full frame or 4/3 bodies that adapt directly to the scope

is it possible to shoot good landscapes with a 4/3 sensor?  Buying 2 bodies is out of my budget

If Swarovski makes an F mount adapter it will attach to any Nikon ever, except maybe the new mirrorless bodies.

None of the AI will work, so you’ll need to know a bit about the exposure triangle:  aperture, shutter speed, and ISO.

Isn't 4 thirds a mirrorless camera?
I'd go with that, but older full frame cameras can be had fairly cheaply too compared to cutting edge tech.
I shoot Canon. The 50d/60d/70D... series is a crop sensor that uses the same mount (EF) that the Canon full frame cameras do.
Look at those too.

Big thing is to get hands on with the camera to make certain the ergonomics work for you.
Example: Hasselblad is a great camera which I essentially cannot stand to use because everything about it is wonky to me. Nikon works so so for me, but Canon fits me just fine.

Same goes for the EF mount.
Good point about "understanding exposure".

I just noticed your signature line.
I do own crampons.