You can afk on pure account by training fishing/woodcutting in F2P.
And yea. Always focus on main first. Thinking of that you can join boss events/raids etc. Pure will need a lot of cash, trust me
P.s or make new F2P account pure. 40 attack, 40 stregth and 50 range. Really good to waste time in wilderness and relax from pvm. You can also do risk fights.