1. Cap ship combos depend on race and if you include the support cruisers. There's too many answers (including many that I haven't found yet) to give a simple answer.
2. Depends on size of opponents / map. Personally I rather enjoyed having all Marza Dreadnaughts in my TEC games, I don't care what cap ship combo was thrown at me, I pick out the biggest threat and smash it fast, then proceed against the next biggest.
3. Depends on your opponent. If I'm fighting Advant and they're using Anima against me I'll go to a 1:2 or 1:3 ratio, sometimes I go only bomber. It also depends on how many anti-fighter Frigates I have, if I've lost mine in combat and replacements aren't back yet I'll take out some bombers for fighters.
4. No, I instead take over planets by culture. You will be assimilated, resistance is futile