Yes you can, but remember the visa starts ticking from the day it's issued, so if you enter after five months, there will be only 4 years and 7 months left
Probably not, but you'd still be at the mercy of the immigration officer when you're re-entering. If he believes you are working illegally in the country, you'll be denied
That's correct. The only downside to border bounces are eventually you will be denied entry on account of trying to live in the country on free tourist entries