We've been fostering for a few years, so far two long term placements and a couple of shorter 'respite' ones to give other fosterers a break.
First was a nightmare, a very damaged 15yo girl with a mission to find every rule, weakness or boundary and drive a dozer through each one. Second has been a (comparative) breeze. Next is anyone's guess.
A couple of observations:
The selection/training process is seemingly endless and grinding, but not as personally intrusive as I'd expected. Form filling, reviews, etc. etc. are a permanent feature - you're a Local Authority employee and it can feel like it. If you change employers - even to a neighbouring LA or an agency operating locally - the whole thing starts again. Perhaps most importantly, where your views and the statutory authority's differ, the casting vote is theirs every time.
Your home ceases to be your personal refuge, it's now also a workspace. How well this balances out depends on lots of things, principally the child ('young person' / 'Looked After Child' - LAC) in question. In some cases - eg abused children - really elaborate routines have to be put in place to keep everyone safe, yourself included (especially).
Every abnormal behaviour from precocious sexuality to violence to Bobby Sands style dirty protest is a possibility, and you can't assume that you'll know what you're getting - incomplete case records, or an emergency care order with no known background, etc.
There are lots of different ways of doing fostering - Long/short term, specific age groups, special programmes of various kinds - and lots of employers, agencies and LAs . Terms vary a lot, from expenses and a small fee to the equivalent of a mid-range nurse's salary. Potentially steady income, and sadly not the kind of work that's going to go away anytime soon.
Really enjoyable at times, hellish at others in short.
There'll certainly be introductory sessions being held by your LA and possibly agencies operating locally. I'd go to a couple and see what you think.