Upload & Sell: Off
A lot of differing opinions, because different people have different priorities.
I would advise you to stay with Nikon and, at least in the beginning, stay with af-s lenses. Except, maybe, the sigma uw.
(95% of nikon users aren't having problems with equipment-look back at trenchmonkeys posts).
Happy users are more likely to be out shooting rather than posting.
Manual focusing, on dslrs, is an acquired taste-you may not like it at all.
Weight IS an issue, even if you are young and strong. Add a pro body and 3 or 4 pro lenses, and you have half the capacity of your backpack even before you add a tripod.
The 7100 would be a great choice, but so would the others-weigh what is important to you with the features of each.
(to me, the feel of a pro body is important-as you get to the smaller bodies, this size, with my large hands, causes pain after extended use.)
The better autofocus will be important to you, especially with animals.
The 70-300 is a very good lens for the price, but the IQ of the 70-200 f4g is much better and it becomes a 300 on a crop body. add a teleconverter (the 2x model 3) and you have a great 600!
You sound like someone to whom quality is important so don't give in to the "they are all good enough for 8x10 and the web". You will take pics that you want to see big!
Good luck, and have a great time!