Your DS I believe is now around 5 months old and you have no other children - do correct me if I'm wrong. While I have come across a few childminders who have just one baby of their own, most childminders I come accross have older children themselves (who are often at school) and thus have some prior experience of caring for young children. Do you have any experience other than caring for your own son for the past 5 months? If not, then think very carefully about if you really want a houseful of kids running about, as while your DS may be easy to handle, other children won't be!
Know what you mean about the office management malarky... I left an office based job before caring for children on a full time basis (though was caring for children on a part-time basis for many years prior to that). You can't manage children like you would manage staff, but being able to organise things well helps a lot, especially if you were dealing with situations at work which required immediate action, thus you very quickly had to formulate an action plan.
Financially, you will need to budget for things to make your home, garden, and vehicle safe for children. You will need to budget for course fees (you will need to do an ICP and First Aid at a minimum, which you may get funded for, or you may not depending on where you live) - contact your local Children's Information Service (CIS) for details about how to become a Childminder and the courses they have available. Some parents will provide a car seat for their child, others won't. Personally I've found it easier buying my own as I then don't have to interchange them on a daily basis - getting car seats in and out of cars is not much fun!
Pay per child varies around the country... where I am on the Surrey/Berkshire border, it can be around £4.50 per child, per hour. However, don't expect to have children all day... often parents will want shorter periods of time.
As you have a young child yourself, try pretending that you are still planning on going back to work and try looking for childcare. Contact CIS for a list of minders and then contact them to find out how much they charge, what facilities they provide, what is and isn't included in the cost, which schools they take to/collect from etc. See what patterns you can spot... and possibly spot things that are not being done which if you did could be your Unique Selling Point. Have you ever been involved in sales, advertising, promotions etc? This sort of 'office' experience can come in real handy, as in childcare and any one-person business, you have to do everything.
Don't expect to get rich quick, being a childcare provider... most of us I would say do it for the love of the job and the chance of pace.