You can register your business name to get a business number, but don't have to. At tax time you claim as a "self-employed child care provider".
For receipts you can just use a receipt book you get at the dollar store. You need to give receipts upon request now (its the law) not just at the end of the year. I have every one pay via EMT so they can print off a copy for their records when they send it, then I do a detailed receipt on my computer at the end of the year or end of care. You can find a sample of my receipt and other daycare related forms at www.homedaycarebusiness.weebly.com

To become a licenced home daycare you need to join a "Licenced Home Daycare Agency" there are good things and bad things in doing this. So I would interview all the agencies in your area. Ask lots of questions, even if you think you know the answer. such as: Can I still take on private clients? When is pay day? (most that I know of pay you on the 15th of the month for the work you did the month before)

Be ready to spend money before they let you join, Dr.'s notes (all people 18+ living in the house, stating you are all okay to run/be around a daycare), TB Tests (all people 18+ living in the house need one), Copies of immunization records (all people no matter their age living in the house), Police Checks (all people 18+ living in the house need one every 3 to 5 years, The law now starts a police check is to be updated every 5 years, but I am hearing that some agencies are going to keep it at every 3 years) and of course references from 3 different people who know you.
As for receipts for any child who is coming to you through the agency, the agency gives them their receipts not you.