You are able to find mounts in the wilderness or purchase them from general stores
You start all the way back to level 1, But you get to unlock mounts earlier, and new legendary mounts.
yes, you get extra characters and mounts
no you can't im afraid. you can ride buffaloes though in multiplayer
yes, along with characters, mounts, challanges, and titles
Yes and u also loose your mounts as well
go on multiplayer and press triangle/y then go through steps u keep golden guns but loose mounts and guns but unlock mounts early
level up. do that by killing players, complete gang hideouts and complete little missions in your journal
you unlock different multiplayer modes such as hardcore etc and you unlock different characters and mounts eg. horses, bulls, ox's etc :)
You unlock the mounts as you progress through the game and you can get new outfits by killing gangs. You usually only get a piece of the total outfit and you need to collect the entire outfit in order to wear it. there is no way to change your character that i know of.
Taxidermist.
This is a riddle. The answer is The Red Sea and The Dead Sea.
There are two, Red Dead Revolver, and Red Dead Redemption and Red Dead Redemption Undead Nightmare