some things i dont get

ok, let me just say that i’m new to the forum and new to the game. I like it alot and play it all the time.
However some things are very vague and i can’t find the information i want. I don’t want to spoil my fun by looking in the walkthrough so here’s what i’m asking. I’m currently in act 2. I just found Lucrecia’s horde.

1. How do you get other ships? I’ve seen alot of other ships and i’m pretty sure i can assume you can get those ships but how? Do i have to capture them in some way? Or do i have to find them? Or do i get them when the game evolves?

2. Whats the case with heat sinks? I traded a beta heat sink instead of my gamma heat sink and now i have a sealed heat sink, but the manual doenst say which one is better. It just says that there are five types but not which five and a list from good to bad or something like that.

3. minor question. How do you turn the stealth module on and off? I can do it with the active sensors and the sigal mask, but not with the module. Since it hinders my manouvrebility, i think its important.

If any of you people are willing to help me (because i’m sure these aren’t the toughest questions) i’m really grateful.