I went through this a few weeks ago building my first PC.
Looked at AMD for cost, fell into Intel by chance due to a friend selling computer parts and needing a new tire. Horse trading.
Part of the deal was an 1151 socket motherboard. I looked at AMD offerings before, but, was underwhelmed. Given your ability to send your motherboard back, I would check Intel. You say $100 for the CPU. What would you have if you send the motherboard back? Equivalent of a board for Intel?
The reason I ask is, can you pick up an equivalent Intel 1151 socket motherboard for the same price? All AMD comparison I've seen are to Has well i3 chips. Depending on the programs, reviews are mixed. I chose an i3 6100 based on my choice of games, locked to one core mostly. How TANE will fare, unknown until this weekend. Trainz is far down my list, TS2009 will do nicely. TANE if decent.
Look at your real needs of what you expect from this computer build. Balance that with the hardware you already have. Mine is built for flight sims first, Trainz second. Video and photo editing on a soon to be replaced Mac desktop and dead Macbook Pro.
Balance your needs.