In my opinion:
I definitely agree with the speed. It should also have a very good point of sail, probably equal to or slightly better than the game's schooners. The gigantic mains'l and Baltimore clipper hull would have given it very good windward performance. For the maneuverability and hold capacity, we should look at the schooner USS Enterprise, and scale the values to reflect the difference in size between the two vessels. The hold should be straightforward: If the Prince is, let's say, 1.3 times larger than the Enterprise by deck length, multiply the capacity by 1.3. If you get them side by side, you should be able to eyeball it well enough.
Since the game will never be as sophisticated as real life, I would suggest making the Prince just as maneuverable as the Enterprise, since its large sail area would have expedited maneuvering. The square sails wouldn't have affected its ability to tack much, since they are mostly rigged on the foremast. I've seen brigantines like the Irving and Exy Johnson tack even more quickly than the schooners they were surrounded by at the time. (I didn't actually see the tack happen. I looked down to coil a line, and when I looked up half a minute later, one was going the in the opposite direction.) It is after all, closer to a brigantine, than a schooner. (the actual name of the rig was simply "Hermaphrodite Brig") Also the beautifully clean run aft would have reduced some of the pressure on the helm, improving handling. If it leans to a silly extent while making a sharp turn, though, it might be a good idea to reduce maneuverability slightly.
The reason I'm comparing the Prince and Enterprise is that they had similar hulls in real life, and both were known for their exceptional sailing characteristics until the Enterprise received a squat little overbuilt brig's rig after the War of 1812. (Another reason to avoid overrigging. Too much top hamper dramatically reduced the speed of formerly fast vessels. I can name several historic examples of that happening. This was generally a problem with the navies after the Napoleonic Era, when they made everything three times as strong, and therefore three times as bulky, as they needed to be.)
Finally, the guns should be somewhere between 12 and 24 pounds, to account for the extra damage done by the carronades, sadly missing in the game. (they could replace culverines, but that would probably take a lot of work) EDIT: ONLY IN COAS