I wouldn't get more than one pleco for that size tank. Plecos are pretty territorial, and you could end up with a nasty fight. Clown plecos are great little fish, but not big algae eaters, they prefer a more meaty diet.
Bristlenose get about 4", I believe. They're kind of strange looking, and not everyone likes the way they look. Apparently they're good algae eaters.
Your 29g looks like it has almost all bottom feeders. You may end up with some unhappiness if there aren't enough caves for everyone.