Re: enough?
I just sold a 17' with 115HP Merc and moved up to a 20' with 200HP Merc. Big difference, but the 115HP did OK for us getting started. It should have no problem getting the under 200 pound folks up on skis or a wakeboard. I did get a guy up on a wakeboard that was 225 lbs, but it was a chore. The most I pulled up on a slalom ski was 165 lbs. I never successfully got up behind it on a slalom at 190 lbs, but I'm also way out of shape and rusty. I am able to get up on the current boat with the 200HP. For tubing, the 115HP did fine with two on the tube, but again... big difference in the 200HP. So it will work for starting out, but IF you get to the point where you want to do bigger people, multiple people, slalom, etc... you may want more.
Also, with a good slalom skier behind the boat, the 17' was moving all over the place when they were cutting back and forth, while the 20' is pretty stable. These were both fish and ski boats with a very low draft, so a bigger deep V boat sitting lower in the water may be different.