MunichMag: sorry, must have missed your posting in Nov., just noticed it now. Here is the answer: yes, if during your waiting period to fullfill the three consecutive years over the threshold you fall below the threshold again, you will have first to crawl back above and then wait a new three years, insane as it may sound. The keyword in the law here is three "consecutive" years.
A major riks lies actually in the possiblity that when changing jobs you could be 1-2 month without gross salary (due to moving or anything like that) and so even if all other 10 monthly salaries before and after the interruption are in excess of the monthly threshold- if you fail to meat the total yearly income threshold through the lack of some monthly salaries, you are still considered to be below the threshold and the game starts all over for three years.
Howard M: if you have been publicly insured before the reduction to part-time, nothing changes with regards to the insurance except your monthly deductions will of course decline in line with the reduction of your gross salary. Your second question I can not answer for certain, though. If your other work is based on a contract/freelancing, than this should not change anything on the insurance side costwise, but if is another employment on salary I would assume that you will receive additional dedcutions from this pay for
health insurance, pension etc as well. But here I am not totally sure and would hope that someone else from the TT-crowd can answer that.
Cheerio