/wall-o-text warning.
I could easily advise a lot of options, but what is you total budget? Are you planning to buy most of a system now, or just start and then have a certain budget per year?
For my income level and unknown future level of interest in photography I __"should"__ start @ $1500 (DX + Kit lens), but I've set my initial purchase @ $2500 (D610 + 20mm f1.8). Although __realistically__ who am I kidding, I'll probably blow $4000+ to start (D810 + (nice zoom) or (2 primes)).
So in a round about, wishy-washy way I'm saying my initial budget would be $2500-4000. With added purchases every so often for accessories and eventually a Macro lens.
I'd probably start with a D810 and 3-4 lenses. 50 MP will benefit most from only the best lenses unless you plan to crop. You'll have to decide on the compromise between versatility (zooms), highest IQ (typically primes), and cost.
Sony might work for you if weight is critical, but the A7 series is still immature. The lens lineup is inconsistent and full of gaps. Some of the lenses are not the greatest, though others are excellent. Most likely you'd need to wait a while for that system to fill out and/or use adapted lenses. Sigma will be producing lenses in FE mount, but that brings the while Sigma baggage. Overall, Sony is probably not the easiest option for somebody not in the game recently.
Buy from B&H or Adorama, etc. Refurbs from Canon are great (12 mo. warranty), but some people don't think Canon is the best bet for landscapes and nature in bad or super-contrast lighting situations. I find the 5DsR will easily work for me, though. Overall Canon probably has the best wide range of fine lenses for an OEM.
Weight not an issue. Not interested in Sony at this point in time. I'll probably never buy a Canon or Nikon lens above the 100mm or 105mm macro size. Well I can conceivably see myself buying an 80-400mm f4.5-5.6 or 100-400mm f4.5-5.6, but realistically any advantage Canon has over Nikon from the 105mm mark and above is a moot point for me. Ultra wide, to wide, to normal, to portrait is all the reach I'll need/want for now.
Yeah, I'll currently leaning toward a (D810 + 20mm f1.8g + 50mm f1.8g) or (D810 + 16-35mm f4) and that would be $1500 more than what I should spend to start. I'd have a bit more wide angle and versatility with the zoom, but I'd lose 2-1/3 stops. Low light/night shots are something I'd like to "play around with" a bit so f1.8 would be nice. Not critical but something to think about.
I wish Nikon would update their 15 year old 14mm f2.8 and lower the price as it's totally not worth the cost when it's only a couple hundred less than the better/sharper 14-24. The 14-24 is least sharp at 24mm @ f2.8 @ corner. And that point is sharper than the 14mm at f4 or f5.6 in the CENTER.
I'd also need a decent tripod, a tabletop tripod, a cheapo "this bag holds crap NOT worth stealing" bag, camera strap/harness that also doesn't yell "please steal me" and a few SD cards (these
64GB SD cards are $35. Or
here.) Those PNY cards seem decent as charted
here. I won't be shooting landscape shots at 5 FPS so speed not a real issue. Capacity, reliability, cost are important.
I avoid 3rd part accessories as I've had some bad experiences with them. Nikon service is one of the worst and they like to claim the user has damaged the camera, especially due to false impacts.
I never use a GPS on the camera. I much prefer to travel with a good trail GPS and then sync the keeper files later. However, a 3rd party GPS is probably unlikely to cause problems as a grip could.
I never use a grip on any camera, though I might with the D810 due to the (modestly) improved framing rate.
Have you considered what will be the backup/second body?
My photography will simply be a hobby with ZERO income generation. In fact it will be a financial drain, so a backup/second body will not be purchased anytime soon or ever. If I stick with it, AND enjoy it, AND can afford it, AND wanted to try something new, I'd buy the next generation body as an upgrade. Or maybe a DX body with something like the new 80-400mm or Tamron/Sigma 150-600mm for wildlife photography, but that's way in the future. Side note. Unless I win the lottery or find a sugar-mamma I'll NEVER, EVER, EVER be able to afford ANY Nikon/Canon Telephoto lens 300+mm or f4.0 or faster. EVER.
I'd want the grip for extra battery power and easier verticals. Plus, I admit it, ePeen, as it makes the camera all big and curvy and sexy. The girls must love your 1Dx. LOL.
I'd want the GPS for Geo Tagging of course. But I'd want to also do some fun things with it. Such as "mount" a camera to my chest and just walk a nature trail and have camera take a shot every 2, 3, 5, 10 seconds or whatever and have a GPS track of the shots. Or mount the camera to an open car window and drive a scenic highway and do the same thing.
When I start to accumulate a collection of "not-total-crap" shots I'd have some prints made at various sizes 8x10, 8x12, 11x14, 12x18, 16x20, 16x24, or 24x36 (assuming a D810, 16x24=300dpi, 24x36=200dpi). Then mount and frame them for a large empty wall I have. A map of SW U.S. with all my shots indexed on it would be cool.
Gotcha, regarding third-party accessories. I'll just spread out the added "bling" over the weeks and months.
And again much thanks for answering my questions.
Holly OCD. I've beed editing this post for 2+ hours. Sigh.