With regards to horsepower levels... I think the best ways of determining whether or not a certain horsepower of outboard will work or not is to either ask a forum such as this and/or see what most boats have that are being sold. Before I bought my 228 Seafarer I asked the same question as well as just looked on websites like Boat Trader and so forth to see what most boats came with in regards to power levels. Most 228 Seafarer's have a 225 hp outboard at the minimum, some of my vintage have F250's on them and then the newer ones were rated up to 300 hp. Having owned my boat for almost 2 years now I can definitely say that I wouldn't want anything less than 225 horsepower as the boat is quite heavy, especially when fully loaded. But, there were a couple of boats for sale at the time that had an F200 on them, I think one might've even had an F150 on it, which again imo is a bit underpowered. I think the same came be said here in the OP's situation where it seems like the general consensus is a minimum of 200 hp and that 150 is likely going to be a bit underpowered, though obviously still doable depending on load, conditions, etc.