Centurion Lightning Stereo Upgrade Questions

[LightningFun]

I have an '04 Centurion Lightning. It has the stock Sony CDX-CA705M headunit and four speakers. It has one battery that's showing it's age (we had to juice it up a few times last summer to start the boat). I plan to install a Bazooka marine subwoofer and a pair of 8" Bazooka Tubbies tower speakers. I have been browsing ebay (search: bazooka marine)

Does anyone have any recomendations for an amp to go with these tower speakers(# of channels, size)? There is a Bazooka amp on ebay near the speaker listings.

I was wondering if a 10" (definitely self-powered for simplicity) sub sounds good(too big for space?) or go 8"? and which amperage would suffice. How exactly should I go about mounting the sub near the driver's foot rest (in front of it? by driver's feet? wedged on top between it and back carpeted board under dash? and should it face towards center of boat or out towards hull?).

For the battery situation, I was considering buying the identical " Exide Nautilus Marine Starting XXHD-M-24 " battery I have (about $50-60) and substituting that in for the old one and using the old one to power the system. Would this work (since there are Deep Cycle type and Marine Starting type batteries)? I was thinking about rigging a $2 switch to open the circuit between the engine battery and the stereo for when the boat is off to not drain the engine battery battery and possibly be stranded in the middle of the lake. An Autozone technician liked the idea especially since a new engine battery would be nice in my situation. I would need to buy another battery case and put that in the obsever-seat storage area. Can this "overload" the alternator? I would appreciate advice on mounting and wiring this battery(right to engine battery leads?) and how exactly to wire this switch setup to preferably get the switch near the driver.

This is a great post about DIY-wiring through the tower. What else do you recommend for plugins and wires for outside the boat/ through the tower? It might be nice to have plugins up by the speakers, also, because our boat sits on a lift all week long at the cabin and it might be nice to pop the speakers off and bring them inside.

I have some digicam pics of the footwell and battery wire mount if that might help anyone.

I am very sorry for the thoroughly complex post but summer is fast approaching and I'd like to put in my orders as soon as I can.......without breaking the bank!

Thank you for your time. I appreciate it guys.