From 1-20 you can't use oak much yet, maybe a little at the top end. Buy a lot of planks (or pick up the spawns to save 100 gp/plank!) and get a whole bunch of steel or better nails, iron fails too much. Go get a saw and hammer (saw's from lumber mill operator east of Varrock, like 10 gp, not much), head to your house, and repeatedly build something till you run out of planks. Bank and repeat. Once you can build something with oak, do it - you don't need nails anymore for oak planks! They do cost 250 each though. As for your other question, yes, it probably requires 30 mining. It's not hard to get, but you might be able to do it with coal off the G.E. - I wouldn't put money on it though.