Best advice Lee would be to talk all this over with your GP. They should be able to give you advice on where to start. Another option after you talk to your GP is to perhaps join a local gym and get some fitness / training advice from the instructors in there.
You might also consider doing some of the organised classes that are on in gyms/leisure centres, but make sure you take advice from your GP or gym instructor about your fitness / training levels etc first.
Gyms / Leisure Centres can be good places to meet new people and get out more. Take things slowly and you'll get there.
I got a really good deal at the time as they had 'ex hire' ones going for around £60. They've all sold out, but you can get a brand new one for £100. I'm a size 12 on my hips, 10 on top, 61kg, 5 foot 6 but went for a large and it fits well. (I tried the medium and my hips seemed too large for it - but if you are a 10 on the hips and of my size it would fit fine I'm sure.)
It is good to try on wetsuits, but you might not get one as cheap as £100 in a shop.
i don't think you'll need much more specialist equipment no - maybe a race belt (or something fashioned to be one) so you don't need to put your number on your front and back. With a race belt (can just be a bit of thick elastic) round your lower chest you put one number on - around the back for the cycle, and around the front for the run.
If you want any more info on sizing for the wetsuit go to the description page on the S2 page, or ask me.