My advice, check if you can't find a second hand mast and boom, that way you save a lot of money seeing as masts tend to (and that is if you don't abuse them like some surfers tend to) last longer then sails so if you really want to invest: invest in the sail and try to find a good second hand deal on masts and booms.
Seeing as you weigh about as much as i do i might be able to give you an idea of the sailrange you'll have. These are off course minimal to maximal ranges, most surfers with big rigs tend to go over what i'll advice you, myself inclueded.
7.0: 14-20 knts
big rigs are hard to uphaul if you don't do it correctly. The bigger the area the more water you'll catch when you crash and if you want to uphail the monstr directly from the water you'll catch a hernia. What i always do, i do it in steps. Rather then pulling the lot strait out i make a sideways motion. i pull the mast towards the nose of my board slowly lifting it out the water, that way the water on the sail will flow off and you can much easier lift the rig from the water.
big sails on sea ... well, that is far from what they're made off but seeing as a lot of slalom competitions are on sea i suppose you can do it. When i use 7.5 > on sea the sea is usually very calm, very little swell or current and enough wind for me to fly out. But if you've got 2 meter waves ... well ... personally i'd get out a small enough board and a middle size sail depending on the windspeeds. But it's hard to say, i have no idea what the conditions really are on the black sea. there's already a big difference between the adriatic sea and the mediterranean sea though both are connected ...
Haiko, AKA crazychemical