It's not the ideal wakeboard boat but if you're a beginner and just want to have fun there are many worse choices you could have made. Still a very cool boat that I'm sure is really fun to drive and can handle rough water better than any inboard wakeboard boat. My mom has a SeaDoo Sportster 150 (15', 215 HP) and that thing can be a blast to drive.
I spent hundreds of hours over the course of many years wake boarding behind aluminum flat boats and center consoles with outboards. This was before the days of ballast and extended pylons were just coming on the scene. None were ideal but me and my friends lived on the water and had tons of fun. Get out there and get time on the board and when you get to the point where there's absolutely no doubt that it's the boat holding you back you can consider getting a different boat. For most people that will take several years unless you're very advanced in another similar board sport and just transitioning to wake boarding (Or you're an advanced gymnast).
I'd ride it as is for the rest of this season and just get comfortable on the board. Learn to ollie the board, ride switch, 180s off the wake, learn to load the line and edge control to get pop, etc. I don't run any ballast for new riders on my boat as it's just a waste of gas. Once you start getting a bit of air off the wake then you can consider ballast. There's probably not a lot of precedent on what you can do in that boat with ballast but I doubt it can handle much additional weight. I'd maybe start with a pair of 300 lb bags. Try putting them in different places but I doubt it will like having both in the rear unless you have a lot of people in the front to offset them. The general rule is 60% of your weight in the rear and 40% in front. 100% in the rear isn't going to fly. If it handles the 300s well you could try putting them both in the rear and then pickup another bag that you could put roughly 400 lbs in under the seats in the bow and see how that performs. I'd guess that's about the max weight you'd be able to put in that boat.
Pair of 300 lb bags:
http://www.wakemakers.com/launch-pad-350-twins.html
500 Lb integrated bow sac:
http://www.wakemakers.com/straight-l...w-bag-500.html
Integrated
Also, an extended swim platform will not do anything for you. The swim platform is out of the water at wakeboard speeds.