It's difficult, The third mission is where you regroup with a shipyard no? If so, your going to be attacked from everywhere. Because of the way the "adaptive ai" works at the end of every mission decomission everything you can (all your fighters and such). The way the adaptation takes place is the computer will analyze your fleet makeup and how many creds you have and build a force more powerful then you and that can counter yours. (so if you have 100 battlecruisers then it'll send 1000 squadrons of Interseptors. I kid you not, I've done that before).
Another cheap trick is to go into the .lua's and copy the stats of one ship a skillion times so that the entire line of stats is repeated. This'll allow you to have some significantly epic battles (like the battlecrusiers vs the interceptors above) and break the population cap.
If your really having trouble start to duplicate the dreadnaught, that sucker murders fighters and does no small portion to cap ships and the ai has no clue what to counter it with.
The way that the quickenings work is that the same quickenings can be bought by everyone, it's just only one person can have each quickening.
and to be on topic, I'm about to start a game of FEAR and Supreme commander (just finished building my new system, 2.8 gig duel core with 4 gigs of ram... only thing holding me back is my graphics card (a gtx 7600)