If you can afford it, I would vote for a single 250-275 HP four-stroke outboard. The weight and power would be about right. Second choice would be a single EFI or DI two-stroke outboard in the same power range - less weight and less money, but will drink more fuel.
The old argument for twins was always tied to reliability - if one goes out, you've got another to get you home. However, today's motors have a level of reliability that really makes a single a very viable offshore option.
Hope this helps - good luck!
