New to me 1996 Blue Water pro-am skier

[samt]

Like the title says I acquired a 1996 blue water pro-am skier. The hull is almost perfect and everything under the hood looks excellent. It is inboard mercuiser 5.7 comp ski. Borg Warner drive 1:1. Stainless 4blade prop. We went out Friday and it's setup perfect for what we do on the lake.
Anyways I'm curious about maintenance. This thing has been sitting in a garage for 2 years. I know the engine oil needs changed. What about drive oil? Raw water pump? Anything else? I'm new to this drive.

 

[samt]

I'm also going to build a tower soon. So any tips on where to mount are appreciated. I simply can't afford a good tower and my brother and I are both too heavy to trust a cheap one.