Check out this year's PYDC
for the modules you can take.
I'm taking 144 CATS this year (normal load is 120, but it's worth doing a bit more if you can handle it to give you a 4% break or so). I did 78 CATS in the first term and 66 CATS this term and 6 next term. I found the workload of 78 a bit tiring.
The following are typical weeks (that was my busiest week last term - I didn't go to all of it mind)
Second term I have less - it's missing about 3 hours but you can get the general idea from it.
Living 30 minutes away from by train - is that to Coventry station. Because then you need to take a bus (the 12) to campus and I'd say that adds an additional 20-30 minutes.
The degree is manageable at the moment (it is a bit frustrating that Analysis, a subject I find quite easy, will take 3 terms to learn when Oxford do it in 2) and obviously there are more difficult modules, but these depend on your preferences and how much work you put into each module. Remember you can also choose modules from PYDC so you can do more Stats/Physics/Logic/Economics modules and try them at the beginning of term and drop them if you don't like it.
This year the STEP grade boundary for STEP I was much higher than the previous 5 years so it caught Warwick out and there was a lack of people to meet the intake (the year above has 325 (not counting drop outs) and we only have 300). So Warwick took some people who got 3s this year. [Last year, 1500 offers were made and 550 put Warwick as a firm (UK/EU students) and an additional 73 firm internationals were made. Yet only 300 people are here now. The STEP/AEA barrier is quite tough (yet not as tough as the Cambridge STEP barrier).
My advice is to take AEA as well as STEP, just as a back up. I found that STEP preparation is quite good for AEA, but go through some past papers for AEA before hand to make sure that you know what is required. Generally they take 8 questions from about 12 topics so there's not a great difference year on year. You only need ~50 to get merit and thus get in here. Regardless, STEP is very useful when preparing for a Maths course at uni so still look at those questions
Have you applied to go to a departmental open day in February or March? Have a look around and find out how long it takes to get to campus from home. No 12 requires exact change (1.50 for a single, 2.90 for return).