Per the GW website the max HP for your boat is 350hp. Whether you choose to do twins or a single main motor is probably your own decision, as I’d think a boat that small you could probably still get away with a single main motor. That being said, I’ve been looking at 228 Seafarers and most of those come with either a 225-250hp single main motor. I’m not sure I’d want a 225hp single main on a boat that is 700lbs more in dry weight compared to a 228.
I think you’d probably want at least a single 250hp main motor if not more like a 350hp single main motor. I’ve never been a big fan of twins because of the cost of having to pay for a second motor, added maintenance because of the second motor as well and then the added weight of a second main motor. Plus most boats with twins aren’t able to plane with a single motor and you have to buy two sets of controls, which makes the cost go up even more. I’ll bet you could probably snag up twin Suzuki 150’s though for less than a Yamaha 250. I think you could probably even get a Suzuki 350 for less than a Yamaha 250. Just depends on whether you want twins or not and what your budget is.