Once you finish your course, you most likely will have a commercial certificate wth instrument rating. In order to take your ATP knowledge test, you must complete a CTP course which costs around $4000-$6000. Once you take your knowledge test, you must meet the ATP requirements within 24 calendar months and pass the ATP practical test or else you will have to retake the ATP knowledge test again. I would recommend that you don't take the ATP knowledge test until you know that you are within 2 years of meeting ATP requirements.
"Frozen" ATPL is not an official term. The term is very rare in the USA. If your plan is to get this so-called Frozen ATPL, your best bet is to go to an EASA approved program.