I'd look at the ported models first, only get a sealed sub if you need the smaller form factor (at SVS SB means sealed, PB ported box, PC ported column). SVS makes very good subs. Auditioning a sub isn't particularly important, especially as your particular room is a great factor (vs some showroom let alone how well the showroom did setup), plus you don't hear subwoofer frequency range like you do a speaker....you can generally go with good test results/specs alone with subs. I've not owned an SVS sub myself, have several others and generally just build my own these days. SVS also has an awesome at-home trial period you can explore.
How subs sound will depend more on your placement, the room and how you integrate the sub (what is your receiver/hardware ?). One sub may work well enough, particularly for just one seat, but room modal issues are generally better addressed by multiple subs. If budget is limited one way is to get one good sub now and save up for another.
Rooms in terms of subs are more about volume than square footage, and whether the room is open to others or sealed to an extent....might try this article on subs vs room size here
https://www.audioholics.com/loudspeaker-design/subwoofer-room-size . If typical 8 ft ceilings, you have a fairly large room there....
Forget about the amp power for now, good subs will have an appropriate amp for their needs generally; without knowing the sensitivity of the system or the impedance characteristics, the wattage of the amp is just not very meaningful.
