Any way you look at it, playing as the Advent is going to be more challenging than playing as the other races. I hardly ever play as them, so the advice I can give you is limited, but here I go:
Its amazing how fast people have forgotten that the Advent has the best military throughout most of Sins' history. That the Vasari now have that title is a very new phenomenon.
Anyways, the Advent's biggest problem is that they have the hardest time getting their long range frigate and unless you macro them to get the most of their side beams they are also the worst. This is what makes them vulnerable to early game rushes. If your opponent is only sending LRFs at you its quite easy to counter since the advent get early carriers (load them with fighters), but most of the time they mix flak as well which is where the problem arises. In this situation there is no real good tactic you can use. If its against the TEC you can attempt to out last them with a battleball, but this doesn't work against the Vasari thanks to phase missiles.
If you can survive to the mid game though your chances start to go up though. Repulsion is still very effective, and Desdras are your most dependable source of fire power (it would be bombers but they don't work well when attacking Vasari planets, though its still quite effective on the defensive) and are less vulnerable to assailant phase missiles (just have some Halycons to keep the bombers away). If the game lasts long enough resurrection is a huge advantage for the Advent as it basically makes capital ships expendable, as you can constantly revive your level 10 capital ships while your opponents need to restart at level 1. But the real challenge is getting that far.
1. .Need help with a start up fleet (e.g Halcyon(s) and disciples )
2.How to counter various rush tactics from Tec and Vasari players whether from long range or short range fleet combinations
3.Right number of repair(sub..carriers) and shield (Guardians..carriers), so far guardians loose out against phase missles but there good against other weapon types. So help me get the right balance?
4. Help me with advent fleet micro-management thats best used during multi-player games.
5. How to use the Animosity/Vengeance combo effectively
6.Is my judgement that a fleet with halcyon (push/craft-bombers) and radiances(detonate anti-matter/armor) best to for cap killings.. maybe a progn for shield reg in there (depending on resources)?
7.Whats best 1-halcyon, 2 radiances, 2 halycon-1 radiance for a starter? Really like radiances detonate antimatter as a cap killer but when do they get 2 strike craft or 3?
8. Best to concentrate on beem upgrades for halycon, defence platforms, and radiance?
9. Beam defense platforms vs Hangers with bombers?
1. You really don't have much variety here. Halycon + disciples is your only real option, with a Progenitor as quickly as possible. Carriers as well if you are faced with a pure LRF spam.
2. Already discussed.
3. It depends a lot on your skill and how many progenitors you have (and what level they are). If you are facing Vasari you won't want many guardians until you have repulsion.
4. If you need to bring out Illuminators, always maneuver them so they have at least two if not three of their side beams firing. It's a lot of work but you need to exploit this to maximize your damage output.
5. First of all, do not do this if there are a lot of phase missile units, otherwise you caps won't last long. Otherwise just form a battleball close to the enemy fleet and use them at will.
6. The Radiance really should not be used much, only in the mid game if your opponent has a lot of capital ships (especially ones that can disable your caps). Halycons and Progenitors will be your main capital ships at all stages of the game.
7. Depends on your situation, but I like to get 1 Halycon and a Progenitor early, the order depends on how fast you have to colonize without running into your enemies.
8. Beam upgrades are not really worth while in multiplayer games, only late game once you have dozens of beam units.
9. Mostly repair platforms with a single hangar to provide shields once you've researched it. Beam platforms are not worthwhile in most cases. Only exception is if you are the eco player and you are attempting rapid expansion.