That is REALLY ambitious of you, which is a really good attitude to have; so keep that attitude. You'll really need it.
That being said, here's some tough love: the odds are very much NOT in your favor to pass all 4 parts in 2 1/2 months. You're setting yourself up for failure if you strive for that. I'm not saying it isn't possible, but it's definitely not realistic. It is very probable, however, for you to pass 1-2 exams during that time period.
It depends on how you want to look at your strategy, some people like getting the “easier” exams out of the way (BEC and AUD) because it's mentally better for them to say “I have 2 out of 4 tests down.” Others want to get the harder exams (REG and FAR) done so they don't have to worry about the 18 month window and they can think that the worst of it is out of the way.
If you were to do the first strategy, I think you could very well get those two done if you really dedicate your time to studying. AUD/BEC are “easier,” but they're not easy, so they do require effort and understanding. But if you do put in the work, it's very possible to pass these two on the first time around.
The second strategy is definitely more difficult and harder to achieve on the first try (this was my strategy at first). There is a lot more material and more complex concepts. But once you do even pass one of these tests, it's like a monster has been slain and it is a big weight of your shoulders.
Personally, I started out with FAR and was lucky enough to pass the first time around. I was glad I started with FAR because there was a decent amount of overlap with AUD and a little overlap in REG (Haven't gotten to BEC, but I'm willing to bet there's a little overlap there too). This helped me understand the concepts better, which made studying a lot easier.
On average, it takes a while for people to pass all 4 parts. I started studying in September and had a plan to take my last test by end of Feb, which didn't happen. So you have to plan for the worst, but don't let that discourage you or let it get in the way of a “best result scenario” from happening.
Also keep in mind that starting in June, they're changing part of the test of tast-based sims to “document based sims.” (This applies to REG, FAR, and AUD) They may be harder or easier but it's just something to keep in mind, because this will be pretty new to any test prep company. Also, I know they extended the testing period for this 2nd quarter going into June, but I'm not sure they will do that for the 3rd quarter, so plan for not being able to take a test in September since it's usually not allowed.
Hope this kind of helps!
FAR - 76 Oct 2015 (Becker)
REG - 87 Apr 2016 (Becker + Ninja MCQ) - 3rd time's the charm!
AUD - 82 Feb 2016 (Becker)
BEC - 85 May 2016 (Becker)