If you go elven, you're going the light armor route. And no, once you get to dragon, you can't keep going over to deadric and back down to dwarven. Have to roll up.
Im conflicted too because I want to make plate... But I want to move to deadric too. I may rank up the whole tree.
That's what I did, up to Orc on the right and Advanced on the Left.
I wish Dwemer armor was stronger, it's my favorite in terms of looks. And even though the Dwarves are technically Elves, their crafstmanship matches Dwarves from other game/literary lore. Plus it's a PAIN to make since you have to lug the heavy pieces back from a ruin and smelt them, so I feel like it should be better than Plate armor at least.