Ultimately - the actual question:
I'm toying with The Idea of A Campaign set around 1,075 where the characters are Darokyn's main allies in turning renegade and becoming Pirates.
Is [stuff] a reasonable absolute minimum fleet for Darokyn?
Easy answer: Yes. I've heard rumours of people starting a successful pirate group in the Reach with just a busted up old Star Guard 200 dTon
Harrier-class.
More useful answer: Need some information first.
1 - Is Darokyn's background and motivation still the same in this campaign?
2 - When in this campaign did Theev come into being?
This basically boils down to: is Darokyn just trying to turn renegade and go "let's be pirates now" or is he specifically trying to end up as one of the Lords of Blacksand? If so, he needs enough ships to go a-pirating on a large scale, but also enough gunpower to stand off any of the other major pirate captains (most notable case being Hroal Irontooth with that bloody pocket warship of his).
Scouts, Corsairs and so on are good at looting stuff from basically unarmed merchants but unless heavily refitted can't take on anything with armour. Type T patrol cruisers (I assume that's what you mean by the corvettes?) are a touch better in equipment but still not really capable warships.
Gazelle-class - if they're packing particle barbettes - can do the job handily, though, and four of them are enough to be more trouble than they're worth to justify fighting.
Honestly, I suspect you're handing way too many resources to the PCs for this campaign. Unless you're asking them to set up Theev from scratch, you've basically handed the PCs two dozen armed starships, including at least 4 'proper' warships and a baby capital ship, and said "there you go" - they basically end up dominating piracy in the Reach by default.
The questions worth looking at in that campaign are more the stages before and after that:
1 - Where are the ship's coming from? Arguably as importantly, where are the crews coming from? The Type Ts and
Gazelles alone run something like 120 trained spacehands, all of whom need to be either persuaded or compelled to join in leaving the imperium and running for the Reach border. Plus, you've got to support them and keep them motivated until you reach the point where you start bringing in money. "
We wants a training day!" and all that.
2 - How are the PC's getting them into the Reach? I mean "via jump space" is an obvious answer and I'm sure someone reading this thread was already thinking that. What I mean is that if you just assemble a fleet of just shy of 9,000 dTons of armed starships, including 8 navy or ex-navy warships, and announce your intention to head to the reach and start pirating merchant ships, you'll have a Navy strike cruiser squadron on your tail before you can say
"Yarrr!".
3 - How do you establish your 'shoreside' resources and alliances (especially if you have deep dark secrets about your origin you need to keep hidden)? What do you do to get a seat at the table if you're too weak and how do you stop everyone else at the table banding together to pre-emptively take you out of the picture if you're too strong?
Ultimately, ship tonnages - even broad descriptions - don't matter that much because 'a 200 dTon armed ship' could be anything from a type A free trader with a pair of beam lasers to a
Harrier-class.