with 400 Eur job per month you should already have your own health insurance - you can only be co-insured for free under your husband's insurance if your average income per month does not exceed 360 EUr/month. If they find out (thru tax note, for isntance) they'll back-charge you accordingly.
If you go/stay with public health insurance, all your income will be counted together for setting the premium of your own public health insurance. You should be aware of this - but you'll also have the option to go with private health insurance which may be cheaper (but you'll need to consider long-term effect of that, too, like if you guys plan to have children in the future).
KSK (Künstlersozialkasse): not sure if you and your work qualify for them. They do also charge you for health insurance, public pension, unemployment insurance etc but at very, very low rates when your income is low, too. But the process of being admitted is long and complicated. Some other Toytowner one put together what is required, I copied it into my files for my clients and put it here again for you to read, too. It is not from me and I have not varified if there were any changes recently, so take it cum granum salis...
Kuenstlersozialkasse really is restricted to ppl earning their money
- creatively, i.e. as visual artists, journalists, writers, photographers, directors, designers etc.
- permanently, i.e. with a view to do this for most of their working lives
- independently. To give an example, in film production, directors and D.o.P.s, video artists and film musicians qualify, while editors do not as KSK thinks they only work under the supervision of directors, not independently.
The KSK form asks non-EU residents to include a residence permit so I suppose they will consider applications from anyone who permanently resides in Germany and is an artist or journalist.
Your operating profit / net earnings need to be in excess of 4800Euros p.a.
As proof of the artistic / journalistic nature of your work, you need to supply them with
- an art or journalism school diploma
- recent contracts with clients (signed less than 12 months ago)
- invoices to clients and bank statements confirming the income (payment slips from a newspaper will also do if you are a journalist)
- current PR material advertising your work
- awards, honors received for your work
- reproductions of your work (i.e. paintings), copies of published material, printouts of websites you designed etc.
- confirmation of membership of an artists' / writers' union
- other proof - i.e. confirmation of several clients that they commission your work as an artist, journalist, writer, director etc
Cheerio