i love collecting all the armor & weapons but i want to level up quicker and was wondering if i do so will i still be able to buy things like iron, fine iron, steel, fine steel, fur, leather, and so on at like level 25 - 35 even if its a b***h to do so.

No. Nearly every item in vanilla Oblivion is leveled to your player. As you level up, the gear sold in shops and the gear enemies wear improves and the old gear disappears. This is by far Oblivion's biggest game play flaw, in my opinion.

You won't be able to buy this but you can work round this if you have the PC version of the game.