What amp should I pair with this subwoofer?

Look for a mono amp that makes around 250 watts RMS at 4 ohms. A larger amp works if you set gain conservatively, but the sub's rating is the ceiling for clean power.

Is it a single or dual voice coil?

It is a single voice coil (SVC) at 4 ohms. That means one wiring option per amp channel, unlike dual-voice-coil subs that can be wired to 2 or 8 ohms.

Sealed or ported box?

Either works. Sealed gives tighter, more controlled bass; ported plays louder around tuning but needs a correctly sized port. DS18's published box specs are the guide.

Can I run two of these on one amp?

Yes, if the amp is stable at 2 ohms. Two 4-ohm SVC subs wired in parallel present a 2-ohm load, so check your amp's 2-ohm RMS rating.

Is 250 watts RMS enough for a daily system?

For most listeners, yes. It fills a car cabin with bass without demanding a big alternator or extra battery, though it won't match high-power competition subs.