Not the foreigner but their landlord, host or hotel need to report any foreigner staying at their property. For those foreigners who need the TM30 for doing business at the immigration its advised to remind your landlord/host/hotel about it. Only in case of owner your own property you need to report yourself.
Comming back from abroad to the same adress doesnt automaticly mean the previous tm30 is still valid. It depends on your local immigration. Some still ask for a update. Some you don't need that.
A re-entry permit does not pauze your 3 months validity of stay. It only keeps it active when leaving. To extend your stay with 1 year you have to be back within the validity period.
Health insurance prices very much depend on many individual factors. What i pay is irrelevant. I might be younger or older. I use max or no deductables. I am healthy or pre existing conditions. Etc etc etc.