I have two major questions and some suggestions for it.

1. RP origin. How can we aquire this mistic RP?
My suggestions is:
Every fraction have some basic personal RP income that not changed.
This income can have some bunuses and modifiers based on conquered territories.
Also conquered territories generates some kind of fraction-wide RP that controled by fraction command.

2. RP distribution. How to spend RP?
My suggestions is:
Personal RP can be spent to lot of things. This discussed lot of times, in general: weapons, ammunition, vehicles.
Fraction RP can be spent by fraction command to: reinforce forposts/bases, transfered to dedicated players for class upgrade (like Chapelans/Termies/Psykers etc).

Would be great to see everyones suggestions about this

RP are for completing objectives and capturing forts\territory that will also provide a steady income.

Also, the 'class upgrade' is one life only.

Offcourse)

Yup.

Plus they have mentioned that Req can come from killing players and Tyranids, and that some locations (mines) can provide resource.

This implies that there will be two tiers of Req, personal and army wide.
Personal is obvious, but army wide Req is probably spent by the war council on orbital strikes and other large strategic calldowns.