I got in as a mature age student (way back when ), but I don't remember having any extra entry requirements, beyond filling in the normal forms. My school results were good and I'm obviously not from o/s, so it may have just been that I didn't need to, but if it can save you any work - for sure ask them! Ask if the SEAS is quicker/easier than the STAT/pi option too.

It's all a bit confuzzling though, from what I can see.

I don't think there's any need to apply now (I take it you're not going for mid-year intake). They only assess all applications once the date has closed, so you may as well wait until you have it all together.