They aren't that comfortable to sit at for extended periods, or even briefly if you are young or old. The bonus is that most people won't spend as much time eating. The downside is that your family interaction may suffer from not spending as much together time at the table.

I disagree. We've had one for 10 years now and spent many hours at it. You can sit at any that you are considering for a bit and have a bit of conversation -- check your messages or whatever, and test the one you are looking at. Like any other furniture, some is very comfortable, some is not.

As for the height, people have counters and islands with 8 foot ceilings, so unless you are incredibly tall and long-bodied, that shouldn't be a limitation.

As for your light fixture, you'll have to measure it. If your table is about 36" in height, you typically want at least 30 inches above the table to the bottom of the fixture. That can vary a bit, but you should have 2 to 2-1/2 feet for a fixture.

Second the notion about them being fine for comfort. If you get hard bar stools, then no, but the right chairs with foot rests work fine.
I, however, hate sitting at the table for more than an hour especially if full of dirty dishes and food. Move the conversation to the living room, and lets get that mess cleared out!

Sorry, can't see the ceiling, but it's 8'. No problems at all.
Comfortable too, and we're not that young. :)