The guages are notoriously inaccurate. My boat does the same, except they read full when full and after emptying they come back up a ways and stay there. Different impellers will not fix the guages, but will help in filling/emptying and not siphoning water in. Don't stress about the guages.
I dunno about total capacity, I presume the capacity sticker is in addition to a fully wet boat (full fuel, factory tanks full), but I've never had a fish cop question me about capacity, nor do I ever run a "slammed" boat.
If you're new to wakeboarding you don't need to worry about additional ballast except for a good surf wake. These boats throw a good enough wake for anyone at an advanced intermediate level. ie: If you can throw a spin or invert you'll be able to do it on factory ballast.
If you're better than that, look into the fly high system for add'l ballast.
Good luck with the new tug. I really wanted a 15, but the 2 is all that will fit in my garage!
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN