Hello,

1. No it does not need rest time, as long as your ambient temperatures are good enough for it to not overheat, maybe you will need to shut it down once in a month or so to remove dust it has sucked into itself... That depends mostly of how dusty the room it is running is. It can run like that for years, for sure longer that it will be profitable to run it.

2. It is good enough

3. No one can tell you for sure, but I am sure it will run for years, again the lower the temperatures the less stress it is for the unit.

4. It can be used for some other SHA 256 crypto, is it more profitable than BTC? I don't think so...

Hope this helps.