Welcome to FT! In response to your question, IMO:

1)I guess the best way to start is to sign up first? It looks like you have not signed up for the challenge yet based on your original post to me. Also check with your employer. A lot of big companies receive complimentary challenge. (Note: you said you work for Big 4 so I am assuming it's Big D, which afaik is the one that has not received the email from AA. See if your EY friend has one...)

2)As for upgrade chance at DFW, all I could say it's YMMV. I had luck as a PLA but no luck as EXP (all DFW - non hub routes). As such, even PP sometimes could be useless in that case. But if it's only 1,250 one way, I personally would not mind sitting at buckhead/MCE, as long as it's not the legacy U.S. fleet...

3)Agree that flying domestic only (especially it's already mid-year) is not enough for EXP, but if you have enough PTO, try to do a milage run for around 25,000 EQM, as EQD is usually sufficient if you do corporate travel. A lot of CX route in PEY, or QR sales from U.S. to Singapore in Business will get you there.