I'd make sure your head unit is absolutely bad. It could cut off because of the way it is wired now. I say this because I still have my factory 06 Kenwood headunit and it works fine, especially if you are using an ipod. Plus, it is a few hundred you can save.
You mentioned wakeboard range sound ... if wake sound is your goal; I'd have to say prioritize your tower. I haven't dug into prices much lately but Kicker makes a 4 speaker hlcd setup that might fit the bill. I'd also look for pics of boats with two tower speakers and strongly consider starting there and building a platform for future upgrades. As far as in boat, amping your current speakers should make a dramatic difference and might be a place you could save money for a year.
I'd decide where you ultimately want your tower to be. Are you the type that will want to upgrade again? Many here can attest to upgrading multiple times and having spent more in the end than if they had done it big the first time. I know I'm one of them.
Are you considering used speakers? There are likely some deals to be had there over the winter. WS 485's are the first to come to mind.