... I'm just excited about getting the camera ...
That is the trap we all fall into.
I did once post about this:
https://petapixel.com/2016/08/24/new-old-vintage-nikons-worst-best-zoom-lenses-compared/
However I have not been cured myself, some people stated I should not save as much money as I do, so I did spent a lot on photography the last months.
To answer some questions:
Not yet able to say how much a D800 would help compared to D750. I have not worked with them.
These are both still top performers. The advantage of D800 is to use some details of your shots as final result, faster way to work then the D750, but probably not that much either.
105 Micro is a good lens, other brand Macro lenses (Tokina, Sigma, Tamron, Zeiss) are excellent as well.
Nikon lenses will be more compatible for the future, have better Auto Focus, ... however they might not be the best choice for you.
I do believe you need a wider lens as well, with a 105 you will need a lot of distance between you and your subject. So if you shoot in a hanger, OK. In a room, probably not.
=> honestly I find this very difficult to grasp and see very little good information.
1) quality is relative, technical testing has its limits, ledgends persist, ...
2) I tend to use myself:
- DXO mark lens tests: effective megapixels with that lens on the D800E
- Lenscore: I mainly look at the resolving power
-
Photozone.de reviews
All this misses in general what people call 3D effect, contrast, colour character, etc... which I fear only your own experience will teach.
Conclusion:
- most of us are as confused as you, there is nothing wrong with that, it is part of the photography experience.
- most of us also put too much attention to camera and lenses and not enough on the way you get effects with light and set up
- some of us are very clear on what is needed, and completely wrong in their beliefs
P.S.: there is so much on the market since it is all useful