electric conversion query

[adwb]

Please can anyone either answer these questions or be so kind as to point me to a source of this info.
I am not a electrical person so it needs to be simple.
The syle of flying is slow scale flying no 3d or high torque stunt moves.

I have just bought a New Z-Power Z50-600/Conversion kit with Phoenix 85 esc to fit to a Raptor 30.
As this kit was originally intended for a Raptor 50 it is supplied with a 9 and a 10 tooth pinion and the choice of the original main gear or a optional extra 86tooth main gear. The recommended battery was a 10s [in other words 36 volt].

I found the comment below from another post and would like some help with the meaning.
"quote"
The main difference is that with the R30, you are going to probably use a smaller pack setup (i.e. – 8s vs. 10s…). Just order the R50 version, add the option for the 86T main gear and I will send you the 85T instead.
"end quote"

what I don't understand is :-
1why is the smaller lower voltage 8s[28.8 volt] pack being suggested?
2 what happens if I use a 10 s pack [already purchased]
3 what gear combination would be correct for a 1os pack? and why?
4 how do work out from a motor spec what is the correct battery size?
5 I also have a devatl 36 volt pack as has been discussed recently and this fully charged measures 45 volts dispite being a 10s
pack why is that for goodness sake?

see why I'm confused and want simple answers?

regards
Alistair