Re: Help please!!!
Keeping a boat outside is fine, but it's more difficult to keep dry. Water is a boat's worst enemy. Needs to be kept covered so rain can't get in, and ventilated so any water that is already in the seat cusions/carpet/stringers (a HUGE issue on watersports boats where the interior gets wet during every use) can quickly evaporate out. The ventilated part is often the most challenging, as a covered boat often traps moisture and later has the potential to cause serious interior rot and mildew problems. Frankly I feel some people's covering methods are more damaging to a boat than if they were to just leave the cover off and let the interior be exposed to the elements every day. At least when it's left open it can dry out in-between rainstorms. But then the sun eats it up. Smart storage is a whole other topic. Get a boat first.
In your price range, I don't think boat brand name matters much. There are hundreds and hundreds of brands. Too much to discuss. For you I say it will be all about condition. Just shop for the boat in the best physical condition, with the largest motor you can afford, within your under $10,000 budget.
3.0L boats in your price range will be a dime a dozen. You can do better. And if you own one for a while, I think you'll eventually figure out why so many of them are for sale for so cheap. So I'd personally recommend skipping a 3.0L motor, strictly based on all your first questions. ESPECIALLY if you intend to run ballast to get a bigger wake. It just won't have enough HP to push a bonus 1,500 pound around while trying to ski and/or wakeboard.
That said, I oersonally owned, skied, and wakeboarded EXTENSIVELY behind an 18 ft 3.0L Rinker for about 6 years before upgrading. It did the job. But my buddies bigger and more powerful boats did it MUCH better, and I ALWAYS wanted to upgrade. And after I finally did, WHAT A DIFFERENCE!! So to others I will always say skip the 3.0L and go straight to something bigger right out of the gate. I think 4.3L at an absolute minimum. And I still think 5.0 and 5.7 is much smarter if you have every intention to option up this boat with tower and ballast like you have said. You'll be stretching your budget though.
Towers can be added to any boat for between $600 and $3,000+. Most do-it-yourselfers seem to add one in the under $1,500 range. Add a few hundred if you plan to pay someone to install it. But it all depends on brand name, quality, and how many accessories you want to add to the tower. Few boats in your price range will be equipped with a tower from the get-go...but maybe you'll get lucky. So use that price range as a guide while you shop. The tower will be another completely different shopping and researching adventure for you. Again, just get a boat first! LOL.
As for your other questions about engine/drive recommendations, I pretty well answered them in my first response. In a perfect world, you can find a 20 to 22 footer with Mercruiser or Volvo I/O, 5.0L or larger, Vortec (96-ish and newer). Steer AWAY from early OMC outdrives. Out of business, difficult to service and get parts for. Therefore they're cheaper and you may find a few in your price range. Then again the last-built OMC outdrives (sometime in the mid-90's?) are actually Volvo SX's with different stickers...they're fine, and can still be serviced easily and are not a problem.
If you find specific boat you are considering, I suggest you ask a new question about it over in the general boating and/or the Mercruiser/Volvo subforums about things to check and whether or not it is a good model. You'll get many more knowledgeable responses over there than you will here in the Wakeboarding forum.
Above all, never forget that my opinions are nothing more than my opinions. Others will vary and maybe flat-out disagree with me, and ultimately only YOU know what you will want. Happy shopping!