1) it doesnt matter, as long as you can use all channels on the amp to power the sub.
2) if the sub is the same, its only the voice coil configuration. If you already have an amp you can pick a suitable sub to get all power out of your amp by loading it correctly. If buying sub and amp, you can go with any combo.
3) i wouldnt go for a boss amp. Unless they have changed in the past years their not exactly good amps. Shallow filters, low power. I would pick a small d-class mono amp from alpine, pioneer, kenwood etc. They are not that much more expensive and usually meet and exceed the power ratings. Being d-class they are also not demanding for current. Just pick a sub with impedance that matches the maximum power output load on the amp and youre done.
Good call on the visual ice stealth box. I love mine with spl dynamics xtr 250d4 and alpine pdx1.1000. The sensitivity in small sealed box is quite low but after some level matching and equalizing its bloody great! Gets really loud, punchy and goes low.