as far as rethreading the top thread, my machine has not been top-threaded anew in 15 years or so. when i see i'm getting close to the end, i attach the next spool, carefully using a square knot, right over left, left over right, and continue. there hasn't NOT been a thread in that machine forever. i gently pull the thread through all the guides, including the needle, and i'm off once again. even when i thoroughly clean it, i just work around it.
oh, of course, if the thread breaks, i do have to start again, and to change a needle, but other than that - never. learned that from my service man.