For attachment, a few options:
- adhesive. They make adhesive just for this.
- Powder Actuated Nails with washers. These are fun. You essentially are shooting nails into the concrete. Probably overkill, though.
- Nothing. One option is to just place them against the wall...maybe hold them with tape, and then just have the interior stud wall hold them against the wall.
Should the pink board touch the floor?
It won't hurt anything.
Should it touch the joists?
Again, it won't hurt anything.
What should I use to seal the between the boards (caulk, foam, teflon tape)?
I've used house wrap tape in the past. Works fine. Another option, price allowing, is to use two thinner layers of foam instead of one thick one and overlap the seams.
You could also leave small gaps between all boards and then come back and fill with expandable foam. That'd give you the most air-tight and insulated envelope.