^As I recall it varies by person. For some, I think like 2 or 3 hours, though the "flash" is more like 10s of minutes. YMMV. Best to start with maybe 7 mg or so to gauge the duration first.
Regarding obtaining rigs, it's easy. I just go to Wal Mart and ask at the pharmacy counter (though I'm the only one of my friends who seems psychologically capable of doing this; not sure why, the worst they'll say is "no"). In some states it's legal, in others, not. In mine I have to sign a needle registry, but don't have to show ID so I can say and sign anything. Even if they changed that, there's internet sources (where you can also get micron filters for like $4 a pop) and needle exchange programs you can get them through for cheap or for free in exchange for old one's. There's no excuse for ever reusing a needle in my opinion.