For the forward bulkhead:

Any suggestions on how to determine an appropriate location?

Put a seat (or piece of foam to pretend it's a seat) where it will be in the finished boat.
Make up a scrap 'dummy bulkhead' (smaller than the real thing) and attach it to a 2x4 a couple of feet long.
Weight the 2x4 so it won't slide around unless you push it.
Get in the boat and push the dummy bulkhead to the correct position for paddling- your knees almost touching the deck-where they will be once yo have the foam thigh padding installed.
Mark the position of the dummy bulkhead.
Put the real bulkhead a couple of inches forward of the marked position - just in case. The slack can be made up with stacked closed cell foam (1/2" thick 'jigsaw' foam floor mats are great for this).
Once you get the right number of foam layers, and have gone for a few paddles to get everything 'pushed into place', Glue (contact cement) a couple of thin foam tabs to the boat and the foam bulkhead to keep everything in place. You don't want those foam pieces floating out the first time you dump the boat in rescue practice. :-)

BTW, you will find it much more comfortable for paddling if you incline the front bulkhead at about 70 degrees or so - the same sort of angle the footboards are placed in surfskis. You can experiment with those angles with the dummy bulkhead.

That's how I've done it on my last couple of boat projects - my 18' Frej and my Mariner Coaster.

Not only does it put the bulkhead in the right spot for a footbrace, it maximizes the forward storage compartment.

(Don't forget the bleeder holes in the bulkheads..)