To be quick:
How will you pay for your training at the ATP school? You say you wish to defer the repayment by attending a university, so I can only assume you are taking out a loan. This seems near impossible to me. It will take a great deal of credit and a co-signer at the least.
Also, in order to defer your repayment on the loans, you must be enrolled full time at a university. It will be impossible to work at a Regional and attend school full time. A Regional requires you work an average of 18-20 days a month. I don't know much about online degrees, and whether taking full time classes online will allow you to defer your student loans, but this seems to be the only marginally possible way in my opinion.
You seem to have a good grasp on the industry. You are right to attempt to get on with a bottom of the bucket Regional as quickly as possible, and a have known a few guys who did what you are attempting after high school. It can be much more costly, and I imagine much more work, but hard work usually pays off.
2 of the 3 Regionals I worked for did not require a degree.
I believe being a CFI for 12-24 months is more realistic.
My background and route:
No money, I worked a part time job in High School to pay for my Private and Instrument.
Attended a well respected state university, and received my BS in Aviation Flight Science using student loans with co-signers for $90,000. My senior year I flight instructed at the school. Since graduating, I have worked for 2 Regionals and a Commuter and was furloughed from the first Regional.
Best of luck,
Tyler