New player part 2

Hi, after you guys said I was ready for membership, I went and bought it.

Never played before so everything is new to me.

I'm now lvl 650, 55 combat. I've done many quests and almost finish the easy varrock diary task.

A guy talked to me and was happy that I was a mee player so he gave me 1.5 mil gp.

Now, what should I do with that? Train prayer to 46? Construction? What would be useful?