It is possible, but you will block access to most of the drawers on one of the bed boxes if you intend the push the bed boxes up against the wall of the room. You will have to set one of the beds out from wall or far enough away from the other so all the drawers can be fully functionally on both beds.

It's definitely a blue color vs black. I think someone else described it as blueberry which I think is accurate. I'd call it a bright navy color, or a mix of royal and navy blue.

Yes, any standard twin headboard can be used with this bed.

This isn't suggested by the manufacture.
The weight capacity of the mates bed is 250lbs. The weight of one bed is 110lbs. It leaves 140lbs.

The inside dimensions for both drawers are:
22.5" L x 4.25" H x 17.5" D

You can buy the headboard separately. The item # from walmart.com is: 3921885.
Link: http://www.walmart.com/catalog/product.do?product_id=3921885

South Shore Furniture
Customer Services: 1-800-290-0465

The front panel of the bed is a piece of wood with 3 cut-outs for the drawer,so I would say no,you could not fit a trundle.

I dont think two of these together will fit a king mattress. Plus not sure the support would be sufficient for that kind of weight.

The matress sits about 2 feet off the floor.
The headboard is about 4 feet high and has lots of shelves-we think it makes the bed look 'finished'
I would highly recommend both products.