Stands for 'Extended Project Qualification', no it isn't an A level but (points-wise) is 'equivalent' to half an A level. I put that in quotation marks because generally when something is referred to as an equivalent in real terms it isn't. They would much rather you have an additional A level than two EPQs, for example.
Basically you take a topic of your choice (but usually you will want to make it relevant to your future degree) and research about the topic to produce a report that can be from 2000-5000ish words. If it's just the report then you'll want it to be on the upper bound in length, but if say you also produce a physical model for an arts&design related project then you can get away with writing less.
Trust me it really won't help your application to do two of them, it just means you'll have less time to revise for your actual exams. One is fine.
Fair enough, it would help in my case as I want to apply to Barts and they look directly at UCAS points for selection for interview but yes I undrstand it'll mean more work
I don't think you can do two at the same time, in much the same way as it's not possible to take two of the same A-level (e.g. you can't enter to do two History A-levels) at one time.