Got a minicat in a trade and need help

Hey everybody,

have been reading on this great forum last couple of days after getting a mk1 Minicat Velocity in a trade,
After being represented in almost every branche of RC, now also into boats :w00t:

The hull is a little damaged, a few little cracks, but nothing beyond repair.
original 3000kv motor and 30a watercooled esc are in there, and they work. but that's it, no servo or battery. Prop is damaged a little.

This is my first boat, en I am sure it wont be the last, so totally took the thing apart just to learn how everything works.
I love tinkering and just wasting my time on rc stuff ;-)

The flexshaft is in good shape, so is the rest of the available hardware. Took the shaft out and greased it already ;)

My questions:

1.
From checking the mount, i can see that a mini servo would fit with a maximum broadt of 32mm. Is that correct?
i can only find on some places on the web that a 18g servo was originally in there, but no dimensions or specs.
Can anyone help or give suggestions for the servo?

2.
I want to repair and paint the hull. It is ABS plastic reinforced with fiberglass, correct? I've sanded it down with 400 grit. Should I repair small cracks by dremeling them out and filling this with epoxy? and what kind of filler can i use for little dimples in the hull? I want to get it totally clean before paintjob.
Furthermore, can i use primer, car paint and a clear top layer?

3.
Is it corect that i would need a Octura 432 or 431 prop for this boat? Or what would you recommend?
Would that fit on the flexshaft that's in there? (assuming that is the original one)
And then the balancing part, how do i do that?

4.
Inside the brasstube (hope this is correct) that leads the flexshaft from motor to prop, there is a plastic tube on the inside. What is the use of the plastic tube?
The coupler between motor en shaft is not alligned correctly, it is a little out of balance, this gives a lot of vibration to the whole boat. I've read that a collet-type coupler would be better. If i look for one 3.2mm (Motor) to 2mm (shaft) do i need to look out for something specific, or would every 3.2mm - 2mm collet coupler work?

Sorry for the many questions and thanks in advance for your help!