Ye, I only intend to use 1 character at a time in raids.

Not many that would allow multiboxing and even if they do then it would be a lot of drama. If they only allow 1 character to get loot (since you are 1 person) then it is pointless also, better to play 1 character at a time but more time consuming and might cause issues with not getting much loot because not being in every raid.

I kinda want to get r13 in phase 2 if possible because of how good the gear is. Similar gear to bwl I think but more pvp focused stats.
12k RP per week for 13 weeks = r13. 11k RP per week for 12 weeks = r12.
Doesn't feel impossible to get r12 or maybe r13 although I expect phase 2 to be max 12 weeks and hard competition for honor.