You seem to be doing good.  Akkans is fine for vs AI matches. Maybe turn off pirates (Set them to inactive in game options) until you get better hand of it?  Getting orbital commerce is good. As far as military, you can't really depend on just 1 kind of ships.  I suggest you get LRMs, and back them up with flak or carriers, and hoshiko.  Eventually get ome kodiaks.

I find get the Kol battleship first paired with a frig colonizer is faster than an Akkan, it has better dps spread. Also try to up the ante against the AI with the pirates first time. They usually never notice the first time, I have only had them get me back once, and this buys you time. Also dont be afraid to use the pirates as experience for your caps later on (just up the ante agianst AI in the pirate screen until threat level say severe two caps can always handle it).

As for diffs

 the TEC have a better eco overall, better armour, better repair ships(hoshiko), and faster ship building. 
 the Advent have better culture effects, better shields, better weapons, mean caps.
 the Vasari have better resource collection, better cap abilites, better frigates and cruisers.

i choose the marza too. But choose anotherone if u want play fair. The marza with his lvl6 ability is just too overpowered for the ai, because teh ai dont stops this ability. with to marzas at lvl 6 j can easily kill complete fleets in seconds. (Please fix this Ironclad).

Just try not to take every planet. Iceplanets and volcanic are very expansie at the startup. U need the research AND u must buildup the planet min. to lvl 2, otherise your new colony costs you to much credits. Asteroids are a much better choice in the beginning.

regarding pirates:

first of all, they get annoying and i turn them off in most of my games, but feel free to leave them on if you like it. just be aware that playing with pirates enabled will in general slow down the pace of the game for all players. makes you play alot more defensively.

second, try to be aware of the route pirates are likely to take from their base to your homeworld. it can be hard to predict in systems with more than 1 pirate base because its easy to forget which base is about to send a fleet. but for 1 base systems its easy to predict. pirates usually just go for the colony closest to their base. 

you can exploit the behavior of the pirate AI pretty easily to dampen the impact they have on you, or at least to buy alot of time. here are some things to take into account

1)  they always bring siege frigates but pirate siege frigates are even more fragile than the regular TEC kind. a few fighter squadrons at a Hangar Defense (2 squadrons works, 4 is best) will clean them out easily. if its an asteroid you don't even need squadrons, just position 3 turrets surrounding the asteroid so their field of fire covers all angles. 

2)  pirates are obsessed with trade ships and will go after them to the exclusion of planetary structures. building a trade port at the world the pirates are most likely to attack will fill the grav well up with trade ships that will distract the pirates for a long time. losing a few trade ships hurts alot less than losing orbital structures. 

3)  a repair platform and a handful of LRMs (like 8 of em) parked next to it can actually fight off most of the pirate raids in the early and even through the midgame. pirate ships are alot weaker than their TEC counterparts, mostly because they have no shields and slightly lower weapon damage. 

I think for your first cap you could pick just about anything but maybe Dunov and get away with it.  Akkan is indeed a great colonizer, though I do just as well with a Kol to kill stuff and Protev to come along and colonize (also of note, Protev can capture extractors at roid belts, Akkan can't).  It's kind of up to you what support you want for your capitals, but if you're not using Kol's flak ability you might want some flak frigs for dealing with fighters.  Generally speaking TEC has a defensive focus, with better armor and more in the way of income-generating abilities.  Vasari favor skirmish warfare, and Advent are fairly balanced but more toward capital-ship warfare.

Also, it may seem counterintuitive but you might find it a bit easier to do an FFA with 2 or 3 easy AIs for your first few games rather than 1v1.  They'll generally play with each other instead of coming after you all the time, including bidding for pirate invasions.