Haha, hardly a wall of text.
Toricredits (also known as TC), are the ingame currency.
Yes you can use mods on a Mac. At the ingame menu, click Setup > Mods then select a mod then click 'load'.
To change your character, got to these forums. At the top, click on Shop. From there, you can buy items to equip your character with.
Btw, the difference between shop and market, is that the market have items being sold by other players, which are generally cheaper than the official shop items.
As for getting better at the game, practise practise practise.
This game is so diverse, it's pretty much impossible to explain to a person how get better at the game in general.
Play around, and when you have difficulty doing a certain thing, come back here and ask for help. Be specific.
Right now, you should avoid doing symmetrical things, meaning, moving the same joints on both sides of the body.