New pirates shipset

[Suicide Junkie]

Well, midlife is your average map.
Ancient will give you an advantage with more places to hide and less trouble from the natives.
Paradise will allow the AIs to spread everywhere, forcing you to use your civilian ship's stealth abilities a lot more.

A pile of starting points will help a lot. I'd say that troops can really be left till later, since the expected returns on investment are realatively low. You do get great profits from a captured colony, but by the time they have enough facilities to be worth taking, the defenses will be fairly tough.
Getting the basics is probably best. Some chemistry/armor, for optimum strength (you can afford to micromanage repairs) and protection for capture ships.
Getting physics for bombardment missiles will help knock down those annoying shields and make things much easier for your boarding parties.

I highly reccommend mines. Not only useful for defense, as a Pirate you can make excellent use of them while on the attack.
Lay down one or two specialty mines in the shipping lanes of some unsuspecting alien race, and then pounce on the disabled ships with a spaceyard ship in tow. You can cap&scrap for instant profit, and build new mines at the same time.
Shield-destroying warheads are among the best to choose for this type of job. Engine disruptors will halt the ship, allowing missiles to be used at optimum effectiveness, and may even disable the weapons if there are no auxiliary supply tanks on board the ship.

Take note! Weapons which require zero supplies per shot WILL continue to fire after the ship is out of supply!
Take great care around ships with pure-energy weapons