Hi Well if your husband isn’t handy you should at least find him handsome.......or is that the other way around?
Anyway, I don’t know your microwave model at all but it seems very strange that opening the door would turn off the clock. Does the clock flash like there was a power failure after opening the door? Does it just go blank? I am wondering if your clock menu has an “energy saving” mode......and if yes try turning that off......might keep the clock on at least. Check your manual if you have one.
Regarding the count down random fail.......does it just stop counting down or does the clock just go blank.....like when you open the door? If it just goes blank maybe the energy save is causing that too? Failing that, it is possible that keypads and clock cct boards fail......so worst case might be a board change out by appliance repair folks. Best I can suggest.