I've taken all of them except Biology to AS and I think, most likely, I'll take all of them to A2.
I thought the workload was fine, but in think it depends on your college/sixth form. With physics and chemistry, we had homework booklets that we had to complete when we had finished a topic, and that was it. Maths and further maths homework was far less regular. At my college, biology was the same for homework as physics/chemistry (I have a lot of friends who took biology, haha)
As for exams, I suppose it depends on how you organise yourself. I had flashcards for physics and chemistry made up before Easter, up to what we had covered (hadn't finished chemistry at that point), and did questions on each topic for both subjects, followed by past papers. Maths and further maths I just did past paper after past paper, but I knew all of the content so it wasn't too bad. It's definitely true that further maths makes maths easier, because anything you cover in maths, you also have to do in further, so you get a lot of practice with the basic techniques.
I had 5 frees a week last year, but that's how the college timetable works. I'd have 9 if I dropped one subject at A2.
Subject difficulty:
Maths, not very - a lot of AS is the top end GCSE, and as I said, further maths made it a lot easier
Further maths, it was alright, but mostly because I did both decision modules, which are both ridiculously easy. FP1 is harder, but it's okay if you put in the practice.
Physics was a lot of maths, so that was okay. Need to know a lot of definitions, and be able to apply everything you know to new situations.
Chemistry also had quite a bit of maths in, but the mark schemes are incredibly picky. You need to know everything, in the way the mark scheme wants it, but if you look at exam questions and mark schemes from the start, you'll get used to it and be fine.
All of them were really interesting, but I think that's more because I love all of them - I wouldn't have chosen anything else.
If you enjoy the subjects, and you are capable of handling all 5 (if that's what you intend to do), then you should be fine. Just stay organised and calm, think about your exams and techniques from the start, and maybe invest in a graphical calculator for maths & further maths (or borrow one from college, if you can), you can check differentiation, integration, use them for looooads of questions and a lot of your answers - a godsend in an exam so you know you haven't made stupid mistakes!
Hope I helped
And apologies for the marathon post!