But yeah, getting into it, I'm sure your aware of what we do with our defensive linemen. The primary responsibility is for them to play the run and eat space and free up space for the outside linebackers to set the edge/rush the passer and for the ILB's to come up the middle and make plays on the run. If they draw a double team, you're OK with that because there's a good chance that means someone from the second level on the front seven will be unblocked and get a free shot at the quarterback and or runningback. At the same time, you don't want a Vince Wilfork type guy. You want someone who can effect plays with their length and athleticism just as much as they can anchor. As Antion mentioned and we all say, Richard Seymour had a Hall of Fame career doing this. At the time when he came out, he was described as being "too tall for a tackle, not fast enough to be a defensive end". As it turns out, that translates incredibly well into being a five technique. Hopefully you get a guy who can effect the plays in the passing game from that spot too, but honestly that's a secondary objective for both me and this team it seems like.
As far as a one gap scheme, you basically look for a 4-3 UT who looks good coming off the edge and running the arch. Their job is to simply beat the tackle in front of them. It's a much faster scheme and is successful on the basis of chaos at the front seven instead of organized confusion like ours. It's a fun scheme to watch actually and has been very effective for some teams.
That's a very basic definition of that stuff, let me know if you need anything more.