1. It depends on which stage you are on at the time. In vanilla Tremulous you can evolve to advanced dragoon during only stage 3.
2. No. Only 3, since a marauder costs 2.
3. It does, but you have to use it effectively. Charging into the alien base thinking you'll be a meat shield isn't a good idea.
4. Yes. On the bottom right of your HUD.
5. You can hit ESC and then Options, and then Controls. Alternately you can change binds through the console. To see what a certain key is bound to you type "/bind [key]" without the quotes. An example would be "/bind x" which will show you what the x key is bound to. To bind something to a key, like a message, you type "/bind j say "Base Under Attack"" without the first set of quotes. You can see what each key is bound to by typing "/bindlist".
6. All human weapons kill structures. You just have to do enough damage to the structure.
7. To send a message to all players, press the t key. To send messages to only your team, press the y key. You can also send messages through the console, which you open and close with the ~ key.
8. If sharing is enabled on a server, you can share credits/evos by opening the console (~ key), and typing "/share [name] [amount]". So an example would be "/share Demo 5". You can also donate credits/evos to the team by typing "/donate [amount]".