SW ships are really, really, really huge. You can make multipurpose ships at low tech levels, they just become massive and slow. But that fits with the Star Destroyer concept well, I'd say.
Go for 50,000 tons. Forget about overhauling, have enough MSP that the ship will survive a decade without overhauling and then scrap it as you replace it with a new one. You'll have to have massive shipyards and definitely improve your shipbuilding rate, as well as use construction factories to fabricate all the components. Otherwise it'll take too long to build.