SOLAR Questions "Newbie"

[Sharko]

I Have a Montana 3830 with a pre-installed 265W and 30A controller with 2- 6V 225Ah AGM batteries.
If I understand correctly a 10 gauge wire has a max capacity of 30amps (used by factory) allows MAX of 365W @ 12V. OR 26A @ 14v if batteries are full.

I want to add 2 more 350W panels. Since the existing wire won't handle this much current how hard is it to pull another wire through roof and fish it through? What size should I run?

With a total of 225Ah in batteries how many watts is over kill, bad for batteries? My combination would make 965W.

I would need a 2nd controller, looking at Victron 50A/100V to run the 2 - 350W in parallel to combat shading. This enough?
Original and NEW panels would be on their own and the 50A controller would be in parallel with my original 30A.
Would this work???
Thanks in advance for any advise.