Upgrading Stereo- Where to start?

A little advice needed for a stereo rookie doing a stereo overhaul.

I'm planning on replacing most/all the stock components of the sounds system in my 04 SANTE over the next couple years. The question is where to start this year? Tower speakers, in-boat speakers, amp/sub?

I'm thinking about starting with some Pro-80's for the tower. I'll have to check the stock kicker amp to see if they'll run them. Is this where I should start anyway?

Any advice greatly appreciated.