Can you go backwards from Dragon to Daedric, so up the light armour side of the tree and down the other, or do you have to head up both sides of the tree? Also, can you get dragon armour perk w/o going up both heavy and light sides?

Cheers.

I do not believe so. At least, UESP doesn't indicate.

Not there yet, but soon will be.

All indicators would say no.
While the graphical tree is spiffy looking, the meat of it is in the 'requirement' section. And for say daedric, that requirement is ebony, not dragonscale, and vice-versa. You would need to go up both sides I expect.

I dont have that many perks in smithing to say definitively though yet.

Can confirm that this is not possible.