It's a hard thing to give great advice on, when you are open to anything. But, with a $7k~$10k budget... it does make things easier.
Before I would dive into the power situation... I need to ask... "How serious are you about wake boarding?" and "How big are the people who will mostly be on the end of the rope?"
Yes... a big v-8 is great... but they drink a lot of fuel, and are generally loud. If this is pure recreation, and you aren't looking to pull a "Pro" wake rider who is 250 Lbs... then there is nothing wrong with an old "Iron Duke" engine. (2.4L GM, making around 120 hp) AND... the GM based 3.0L V-6 is smooth as silk, and makes long rides very enjoyable.
Outboards and jets are easier to get started with... but if you are looking at an I/O... then I would stick with engines that are GM based !! Over the years, there were some very goofy bastard engines that Mercury came up with. One was HALF of a ford V-8. With engines like these... there are almost no parts available. As far as outdrives... look for Mercury Bravo or Alpha. They are common, and parts are out there.
Here's a list of I/O questions to ask about...
1) When were the water pumps/impellers changed?
2) When was the drive shaft rebuilt? (pulling the engine is a pain in most of these)
3) When was the bellows replaced? (boat will sink when it rips)
Unlike a jet... you can't start them dry. If you do... you will wear the water pump very quick. (They are rubber impellers) SO... you MUST take it for a real water ride with the kind of $$$ you are looking at.
There's really no right or wrong with a starter boat... and even though you may have something in mind, on how it will get used... that may change. (ie. the guy who wanted to wake board decides they don't like it)
Then... finally... don't get stuck on a brand. Look at the drive. A big name could have a goofy engine... and that will make service hard.
I know most of that was fluff... but that's because if hard to nail down what you need right now. BUT... to me... more than power, or a name... let's talk space. (The most important thing)
Physical size: Personally... I would recommend the biggest boat you can Physically deal with. Both with weight (for towing) and length. Think about where you will need to park it, and the entrance to that spot. You may want a 22' boat... but you may find that (with the trailer) an 18' boat is all you can park. Also keep in mind that boats get heavy, so if you need to stick it in a tight spot... it's not going to be like your skis, where you can simply roll it in by hand. (I can't even move mine without power, and I use my tractor or RZR to park it for winter, because my truck just doesn't fit)
People: Just like with a jetski... the "allowed" capacity isn't the "Comfortable" capacity. For example... my Islandia is rated for 12 passengers. BUT... anything more than 7~8... It's getting crowed, for an enjoyable day. (that's also assuming 3~4 kids) If you have a daughter who wants to lay out and sun herself... then that will take 3/4 passengers worth of space. (lounging/lying on a seat) If we take that thought into effect... if you get a 19' open bow, and it's good for 8 people... then any more than 5 people... and you will be having to move out of each other's way to do the basics. (2 people up in the bow, driver, and 2 in the rear) Also... if you have the weight of 4 people in the boat (with food and gear for the day) and are trying to tow a skier... then it will make it hard. A bigger boat (not necessarily more power) will help in this case, since it has more floatation, and your hull won't be sunk down.
Dry Ride: Here again... more size will help keep you dry. Some days that's not even a thought... but if you get out to a choppy lake, during a vacation... and you want to use the boat to go a few miles up to a restaurant... you don't want to be wet. Also... some lakes have size requirements with lifejackets. Deep Creek MD has a law saying passengers under 12 years must wear a life jacket on a boat less than 21'. AND, then, when over... there must be grab rails installed. (here's one more reason for bigger)
With all that said... I personally think the seadoo islandia (or similar deck boat) is the ideal "Do all" family boat. It's big enough to stay dry, it's small enough that I can still handle it alone if I want... there's enough room for 2 normal families to be on it... and has enough power to pull most water sports toys. (plus it has a sink with fresh water, and a potty for the girls)
That's my story and I'm sticking to it.
But if you want water sports then I agree with what was said above can't go wrong with a 3.0L have been around forever and run well!
