Excelsior

Wondering what the backpack and bank item and weight limits are at their maximum. i.e How many of the deeds do you need to max them out?

Also, for bonus points, (I'm sure I already know the answer, but just confirming): If I relayer a weapon to say platemail arms, do those plate arms count as having "mage armor" for the sake of meditation and regen purposes?

I believe the plate arms do not count as mage armour for med purposes. Also if I recall correctly think the max is eithe 400 or 500 items for the backpack/bank.

-Iago

Backpack limit is definitely 500, just got there myself recently. Fairly certain bank box limit can be raised to 500 as well, only raised to 200 so far & some time ago. When you try and use one deed it tells you what the limit is so you don't waste it if already at cap.
With respect to relayers - I thought the item was effectively "destroyed" just keeping the "look" of the original. Not sure about meditation though as I have only relayered items to leather types.

Ok, feeling confident on the number 500 for item count of bank and backpack.

What about weight limit?
And if anyone else can weigh in on the relayer question that would be good too...

I *think* that the relayer won't count against you as a relayer of say an axe to a plate mail arms. The game still sees these items as the item they were initially. so it isn't reading them as plate mail per say its seeing it as sewing an axe to your arms (if that makes sense).

The backpack and bank item limit is 500 each, and the weight limit goes up to 1000.

And, to simplify the relayer question/answer...

The item that you want to turn into a relayer takes the form of whatever your sample item is. The sample item (in this case, platemail arms) is purely cosmetic, meaning that anything and everything underneath the name of the item will be replaced with the stats, boosts, regens, etc. of the item that you are actually relayering.