Originally Posted by PLECO
the guy at the fish store said that all his plecos only grow about 4-5 inches but if i dont get that i guest i would get a oto probably. but would i need more then one. the tank is pretty much new only put the betta in a few days ago. so to cycle it i guest i would put gold fish in it or can i put a few dalmation lyre taild mollys in it
What kind of plecos does your LFS have? I've got clown plecos in several of my 12g tanks (including a betta tank) and they only get to 4".
Gouramis and Bettas are both anabantids and likely to not get along. Likewise, the guppy will likely attract the attention of the betta.
The otos will be fine, just make sure the tank is fully cycled before they get added.
You can use a liquid testkit to know how long it will take your tank to cycle. A betta with some plants will do ok to get the tank going on the cycle, just keep testing every couple of days and do appropriate water changes as you see the nitrite/ammonia spikes.