We have a 2 story family room and we are wanting to convert the room into 2 rooms. By adding a ceiling/floor. I would like to contract the framing the ceiling out and I would do the sheetrock and flooring and HVAC and wiring.

Here on some specs on the room: 13x17.

I assume the joint will run on the 13' wall. Here is the problem. The HVAC vent is where the ledger would go. Below are pics:

How would I run the HVAC?

I just want to make sure that I am educated before talking to the contractor. The other questions that I have are what size lag bolts would be used to connect the ledger to the studs? Also, would you use a lag bolt on every stud? Also, on the floor joints how far would I space them? 12" or 16"?

Thanks in advance,