I do full-on pirate mode playthrough very often, -100 relations with everyone pirates included, here's some tips.
Skills
You need safety procedures and field repairs in the industry tree. Maxing those two branches makes raiding much more profitable, as 1. E-burn costs no supplies 2. lower maintenance 3. recovered ships have a significant amount of hull + CR when recovered which means they scuttle for ALOT more.
Your starting skills should definitely be at least 1 point into field repairs, as that effectively doubles the supply loot from a single recovered ship.
Some other things that are essential. Navigation + Sensor skills are super important. Navigation level 3 is huge, as it allows you to fly faster and also transverse jump. 11 burn is actually really important because it means you are at the same speed as most AI fleets (due to their nav relays in the campaign). Simultaneously, transverse jump means you can jump in and out of a system from anywhere. A lot of systems have inner jump points that are well guarded so transverse jump is basically a requirement for systems like Sindria.
Sensor skill level 2 is extremely powerful. Go Dark basically makes you invisible with sensor 2.
Making Money and getting ships
You basically want to stick to frigates until you can find a market to buy augmented engines from. Stick to systems with tri-tachyon free ports, independents, or pirate bases, because they won't care if you have beacon on or off. Even if you are hostile to them, they will not chase you unless you turn beacon on. Typically, I like to base out of Cethelen and farm tr-tech fleets for carriers and organ smugglers. Alternatively, basing out of the abandoned station near Salamanca is great, because the league fleets there are basically free farm. Supplies are also relatively cheap at Cethelen, because they don't get shortages like pirates do. And if you intercept a drug smuggler, you can dump your wares right at Qaras for a huge 150k payday.
Make sure YOU HACK NAV RELAYS!!!! IF YOU DON'T, AI WILL BURN FASTER THAN YOU. YOU WILL DIE!
Also, you can run drugs and organs between free ports and Qaras. Tends to be pretty profitable albeit boring.
You'll want to be really attentive to smugglers. Kill them with impunity to get money.
You don't need to have actual friendly relations with any pirates. Their military markets are worthless so don't bother. Kill pirate convoys as well for farm.
Key Progression points
Getting augmented drive field is basically game-winning, as it allows you to fly cruisers at 10 burn. From that point on its just a matter of spamming a bunch of carriers you stole from battles.
Make sure you develop a habit of looking at every single black market you can find. Buy a ton of the weapons you like to have for your ships at every opportunity. Also, don't sell all the weapons you recover from battles; build up an arsenal by storing them in Abandoned station near Salamanca. You'll want to reach a point where your storage station has every type of weapon available.
You're going to find that money will not be a challenge. The biggest challenges are getting good ships that you can pilot because you have no access to any markets. Personally, I use a restored luddic path lasher, then a hammerhead (or a medusa if I get lucky with a tri-tech fleet that has it), then a typically a conquest as they are readily available. You can pick one easily visiting any nearby Sindria Diktat system and destroying their out-of-system patrol. Conquests are great because with augmented drives, they still fly at 10 burn. Meaning you can still run a 10 burn fleet. If you get lucky with d-mods, like having structural problems or unreliable subsystems, your conquest will even be extra cheap to fly as well.
Once you are confident enough to build your own colony, do so in a core system. because the -60% accessibility from hostile plus -30% from distance really hurts. Cool strategy is to burn an AI colony to the ground and build your own. Great targets are Luddic path colonies, good habitability. Do not orbital bombard the planet, as pollution penalty is severe. Raid the planet repeatedly until it decivilizes, then colonize it, then abandone it (to remove decivilized), then colonize it again for a pristine condition core system planet.
After your first colony game is basically won.