Hello, complete newbie here. My wife and I are going on a trip March 18, booked with AA. I have 71k miles. The flights are PHL -> DFW -> HND, and returning HND -> LAX -> PHL. The tickets were a bit under $1600 each. I'm wondering if I'd be able to actually use my miles somehow? I was looking on the aa website and it would take a little over 91k miles to cover one person. I would have to spend about $650 to buy the 20k miles needed to cover that.

My hypothetical plan is:
1. refund my existing tickets (mine, not my wife's) for a travel credit. (I believe I got the kind that you can do that)
2. use my travel credit to buy the 20k miles (~$650)
3. purchase the tickets for myself with those ~91k miles
4. choose the same seats as my previous ticket had, next to my wife

My questions are:
- does that plan seem reasonable?
- can I use travel credits to buy miles? (step 2)
- could I reasonably guarantee that I could get the same seat next to my wife? she is claustrophobic and would refuse to go if we don't sit together