Hi there & welcome
You're already ahead of the field given your experience in accounting. I personally found it far easier (and got better quality and more interesting clients) having a solid background in all areas of accounting.
Do you have experience in small business accounting packages? Get a hold of some trial versions of the most popular ones (QuickBooks comes to mind) and have a play with it. Consider attending a training course on it, unless you're a bit of a systems whiz. I know it would have helped me (instead of the fake it till you make it approach).
The best source of business I found was to approach accountancy firms, as they often outsource or recommend onsite bookkeeping services to their clients. Be careful to stress that you are not looking to take their clients away, just offering a complementary service. You'll find it a great advantage in being able to talk their language too.
As for charging, what I did was ring up local bookkeeping services as a potential client, and subtly asking what their rates were. It surprised me how many just answered the question without first establishing that I actually *was* a potential client. I purposely positioned myself at the higher end of hourly rates, as I am a fully qualified accountant, rather than a bookkeeper without qualifications.
It took me around 6 months of networking and meeting with accounting firms before I had a full diary, and 10 years on, still have many of those original clients.
Good luck!
Meredith