It's probablly just bad luck. If you're just training, you could just stick with bronze since they're cheaper and you seem to have better luck with them.
It's one time experience. Once your tree is fully grown, you check it's health to see if it's healthy. Afterwards, you can chop it (pick it for fruit trees) or chop it down.
If you do want to do armour, I think dhide (t) and (g) is ok. The forums on the main site have sellers selling for much cheaper than buyers in world 1. But these was a while ago, I don't know what the demand for green dhide (t)/(g) in F2P is anymore
1) Don't think so. 2) Most likely not. 3) For the win 4) It's a leet (1337) way of saying please. Sorry for my vague answers for 1 & 2, I'm not certain lol.