Should I have 1, 2 or 3 cell training rooms?

It's up to you how many Dwellers you want assign to one room/ability, also each room takes "Power" so be ready

I have a single wide room for all of them except the Game Room which is two wide. If I place one Dweller in them and a Radroach attack breaks out then they can handle it. Honestly I don't usually have the manpower to have all the rooms manned and put people in the Training rooms even with about 118 Dwellers. Until I have a larger population I'm sticking with single wide rooms.

Two rooms wide seems to be perfect for me. I'm also getting new dwellers and I usually send them to a skill room first.

I prefer to hold rooms to doubles when I can.

I have double the number of luck training rooms as any of the others everyone needs luck it increases chances of a rush working and explorers finding stuff it helps in fighting rad roaches as you get more critical hits (not sure if dwellers get them but guns have a varied fire power I want the max ) I have 72 dwellers and 20 training spaces they are always full and 8 of the spaces are for luck.

I am at 102 % occupation so all my rooms are full and I have a few walking around.