Freelancers! ANobAG vs PayrollPlus : how much difference am I looking at really?

I'm getting an offer for 30 days of work spread out across 6 months, Jan-July (potentially more). I'm really glad this is happening - after many personal setbacks. I haven't done freelancing before, but I do have hopes this is the start. I'm aware of the risk of mis-classification etc with a single-client, having read up about it.

I understand that ANobAG is more of a headache due to the paperwork. Costwise though, how can I realistically see the difference from say Payrollplus? How can I know if ANobAG is worth it, besides just feeling that it looks daunting, or whether I would rather invest that time into branding/positioning myself as an entrepreneur to attract further clients? How much does Payrollplus charge, and what % of my day rate can I really expect to keep for myself?

Further, is it possible to later on register myself as a freelancer, if I get my second and third client? Or does using something like Payrollplus in any way negatively impact such a possibility?

Thanks in advance for your advice.