just check out some of the replays on gpgnet mate, there are hundreds on there and you can watch the game unfold from other plays to get good strategy and tips for base building. it certainly helped me.
that really depends on the base you are attacking. any base with t3 matrices and feeble defences deserves to get blowed up. bearing in mind that i genreally have at least 10-20 air sup patrolling my base, as well as SAM and flak cannons, as well as mobile flak. 20 gunships may not make as big an impact as you might think. yeh it might take a few fabs down, but how much did you spend making those 20 gunships.
im not saying its not beatable, everything is with one tactic or another. but to build big you need an economy to do so, one of the best matrices is the 1 t3 gen and 2 t3 fabs. if they get taken out you only lost 2 fabs and not an entire economy. as for the larger t3 matrices, once you have the ability to make them like that you have the ability to defend them. you could say for anything that its nothing X amount of X unit wont get past but its all a question of decisions. if you are making 20 t3 gunships i have time to build a load of SAMs and mobile sheild gens. if you are making nukes i have time to make anti nukes.
thats why the game is great, you can counter my X with your Y, but then i can use some Z to beat that and so on.