And keep in mind that the initial idea of freighters is to generate money, so the more expensive the freighter, the less economical.
sorry the idea of frieghters in da is diplomatic not cash
Wrong.
It depends on the game setting.
If you've got hundreds of throwaway planets at your disposal, even a maximized trade array with as many Economic Starbases as you can fit won't be worth that much.
If you've got a Medium Galaxy with Rare Stars and Rare Planets, you'll probably have to make do with only your home system until you conquer other worlds, and even then, you won't have many planets. Here, if you create a trade array of all your trade routes covering the same path, with 4 Economic Starbases per sector, and each with 3 trade modules, then trade will become a major part of your income.
I think you would definately be able to build the galactic privateer much earlier in the game before you can build single freighters powerful enough that can withstand enemy fleets. If a Stupid AI manages to build the Galactic privateer before you, then in that case i might say, "go for it"!
No, even if someone got Privateer before me, I wouldn't make 'Battlefreighters'. It would be better to just keep a fleet of real warships to patrol the route.
The very, very impractical hypothetical plan I was thinking of and will never execute is this: Get Galactic Privateer
and make Super-Dreadnought Battlefreighters armed with nothing but a Trade Module and lots and lots of weapons(no defenses, no engines).
Then, if Peacekeepers or Mega-Pirates strike, it would be fun to watch them attack your invincible super-freighters and get blown to bits. But other than that, there's no use. It would just be a deathtrap to bait in enemy ships and get them killed.