1) if you can place it, there should be enough depth inside the shipyard. But if the seafloor goes up at the front, your ship may still crash on release.
2) you can put cannons on the upper deck
3) For sails you can mix and match anything that fits. Brig has 8.6 sail capacity iirc and Large Speed Sails take 2.7 while medium take 1.7.
5 Medium Sails take a lot of space and are harder to manage than 3 large.