Got it, time is the biggest factor,sometimes I dont have that long to comit to a game.Ican usually beat the hard AI unless I really screwup, never played unfair before.

I've played against the AI a whole bunch, and while I have no MP experience, I've watched a lot of videos/replays of 5v5's so I have some general idea of how they are played.  I can tell you, the two are almost nothing alike.  The AI can get you used to the game, you can learn how to colonize fast, but after that, the AI plays very differently.  I can beat unfair and cruel pretty consistently (although cruel drags on too much, the AI rebuilds their whole fleet for each planet you take), and yet the strategies used (expand towards them then starbase the front line planet) would utterly fail in MP.

If I were gonna play against the AI for the sake of learning how to play MP here's some things I'd do.

• Play with all settings on fastest, this seems to be a standard for MP and it takes some getting used to, since the game goes way faster with it, you have less time to react to things.
• Learn to colonize fast and with minimal ships (astroids can be done with just a colony).  In MP your fleet might be needed elsewhere but you need to make sure you still expand.
• Build a large fleet early, most of your early game resources should go into a fleet and infrastructure needed to build it, not long term investments like research (some research should obviously still be done, the colonization techs, fleet size techs, and whatever techs are key/very strong early game for your faction)
• Don't rely on starbases.  They work really well vs the AI, but you don't want to get used to that crutch since their uses are much more limited in MP.  In the games I saw, they mostly weren't built until later except by some Vasari.
• Scout often to know where the enemy fleet is.  Even the AI tends to keep most of it's fleet together so you can still scout to see the AI's fleet movements.  In MP you always want to know where the enemy fleet is so you can react in time.

Again, I have not played MP, only seen others do it.  These were all 5v5 skilled games, which is sort of a subset of MP (but one very popular on the forums it seems), so if that's what you're looking for I'm sure some regulars can say a lot more about it.

Yeah there are some Tactics which are common in multiplayer because they simply are the most proven.

• You genraly only start with an colonizer cap since they give you an quick expansion boost.
• The only common exception to the above rule is the marza dreadnought(learn to fear an level 6 marza)
• Like it or not. there comes an certain point in game where your capital ships will die in a minute don't rely on them to much
• Learn the rock paper scissors lizard spock of sins. if the enemy got a fleet of long range frigates build corvettes to counter them if the enemy got a fleet of mainly corvetes build flak frigates to counter them. to counter flak  build light frigates. and to counter lf buildt long range frigates.

Here is an basic report of standard skilled game.

Early game- send out 4-5 soucts to find the enemy 
Quick colonize nearby planets since tax from polplation will form the base of your economy.
Spend a large chunk of your income on frigates dont build a second cap until your first one is level 6 is a good noob rule.
a fleet of let say 60 to 100 frigates is a strong fleet that will be able to take out the cap of a simliar fleet without suffering major loses is the point where you go to the mid game.

mid-game the strength of the early -game fleet is depend on some factor like the number of planets you could colinze ANd how much you where willing to spend on your early fleet.
In the early game out numbering the opponent by 2 to 1  would have meant victory for sure. However in the midgame people will have build defenses that will provide ways of winning lost battleses.  
3 frigate factory + 2 repair stations will give your fleet an excelent fighting change against a superior opponent. because hey if you can create 30 Corvette's in 20 seconds who needs suprior numbers.

Late-game
Is mostly just an game of who has the most bombers. 

Yup, best way to find newish players is to make small or medium games, even if you don't advertise it in the title. The hard core pros rarely join such a game.

Vasari Skirantra's also also an acceptable starter.

I haven't seen a skirantra lead in a very long time....it is pretty much entirely space eggs now....

Difference between Kortul and Space egg is that a Kortul can be useful late game even at low levels...space egg on the other hand has a very nice lvl 6 ability...

Egg is also better for SB rushing...you can freeze fleeing units and more importantly, colonize planets efficiently...Orky spam is quite common as Vasari, because you can spam Orkies and defend a large amount of territory while minimizing your fleet upkeep...even frontliner Vasari players can build a few key orkies and then send the egg to colonize center, putting them in a much better position...

Migrators also are limited by AM while egg is not so much...helps you rush far flung planets and colonize them so that your SBs build/upgrade faster....

Other Vasari caps just aren't as conducive to that strategy...

Ironically, TEC leads are more diverse than Vasari leads...

I've seen HuyMac lead with 8 skirantras before so....yeah.....

Happens to be an excellent Wail counter too....

and phase missile bombers take care of anything the Advent can field.

You don't?!