I agree about the acoustics importance.
also, you'd have to experiment with hanging the sub, but I would say
it's best to buy a sub in a size you can afford to put on the floor because it's
quite likely that it will sound best..
I don't have a model recomondation, but if you know some similar bars with the sound you're looking for you can just ask / look what they have.
about the ohmage issue, you can usually adjust the resistance by planning your serial / parallel connections.
you can use this formula to check if this apllies to your situation.
(the text in this article is strange but the formulas are correct)
there is also a topic about this in the forum, but I'm without hebrew font so I can't find it right now.