As an independant foreigner you can only be an employee. If married to a German you can work independantly. Getting a work visa should however be OK as a foreigner, typically start with a 3 month tourist visa during which time you complete details for the work visa. Health Insurance is compulsory, make sure you arrive with some, and you have to arrange it. As an employee it is a government scheme tied in with your wages, if self emplyed you can organise your own private insurance.
To practice in De you must be a Heilpraktiker (examination like medical board exams). Some DCs have managed to legally obtain their HP without an exam, this is possible in Mainz (Rhineland-Pfalz). You need a raft of paperwork and a residential address there to apply. Be aware that it is not certain that this restricted (eingeschränkt) HP will be recognised in each other states (Bundesländer) Working without a HP licence carries significant risk. The HP exam runs twice a year, difficult 60Q multichoice and an oral exam all in German. You register with the local Gesundheitsamt (Health Dept office), either based on your registered residential address, or where you intend to work. A full HP allows you to work everywhere in De. Once you have the HP it is valid for life.
Germany's history with 'chiropraktik' is long and convoluted. ChiropracTIC has a bright future, supported by a large group of HPs and DCs. Professional Indemnity insurance (Haftpflichtversicherung) is not compulsory, but should only cost around €350/yr