It should be okay to clean all of your computer with isopropyl alchohol. The alchohol vaporises at room temperature, so just make sure it is completely dry before connecting the power again. I'd be carefull which paper towels you use, as some paper towels tend to leave behind small traces of paper.
I usually use a cotton but when cleaning my computers.
It is, but I can't see it fixing that gpu it looks fucked. I'd take it apart entirely and give the entire thing a full clean and re paste of thermal paste and even than I'm doubtful make sure it's 90%+ other wise the other other % is water.
