According to Sundance's website for the 2016, 150HP is the max and 115HP is the recommended. The performance bulletin on that boat says with the 115 she'll make about 30MPH at 4500RPM with two people on board..
You can pretty much tube behind anything that moves ... how fast it moves determines how much of a back-beater the tube ride is, but that boat'll pull a tube well enough. With two people on board, she'd do fine for a wakeboard or kneeboard. Those are slower slushier rides anyway. With 6 or 7 on board, I think you'd still pull okay but without trying, who knows?
Skiing is a different bag. It'll pull a skier fine, but I used to like to slalom at about 30MPH. You're gonna' have a hard time generating that with 6 people on board. It's a big flat boat, so it looks like it'll plane fast enough to get things moving, but I don't know that the ride will be a good one for a slalom skier. It'll pull ya' on two sticks, but again with 6 people one board who knows how slushy it'll be.