6 Speaker Boat System

Ok guy here what I got and need some assistance
I bought a new boat and the previous owner had 6 speakers installed
2 in the cabin , 2 in the cookpit and 2 on the bridge
The head unit is a Clarion M475 and the amp is a Mempis PR 4400 4 channel
I do not like this set up and have installed a new separate unit on the bridge and rewired the bridge speakers to that unit so they are no longer part of the old system
I would like to install 4 new speakers ( Bose 161) in the cabin and leave the existing speakers ( poly-planar MA-905) in the cookpit
I would like to be able to use the fader from inside to outside so when the wife wants to go to bed I will be able to shutoff the cabin speakers and still have music outside in the cookpit also when we are hangin in the cabin late at night I could shut off the outside speakers so not to disturb other boaters
Questions….
Do I wire the inside speakers as the front or rear and/or does it make any difference?
Do I wire the 4 Cabin speakers in series or parallel, to channels 1 and 2 and the 2 cookpit speakers to channels 3 and 4? Does it matter which channels I use?
I am assuming that channels 1 and 2 are the front and 3 and 4 are the rear so I am thinking I should wire the 4 cabin speakers in parallel to channels 1 and 2 and the outside speakers to channels 3 and 4.
Now here the hard part, how if at all possible can I add a sub? Do I need a separate amp?

Thank You for any and all input
SS