Are you going to go planted with this? If you want any fry to have a hope of surviving, plants may be a necessity. They call nagas grass (a floating plant similar to very fine-leaved hornwort) guppy grass because it's as prolific as guppies (growing very fast with many branchings) and because it makes a great camoflage for baby guppies. Java moss, or thick stands of fine-leaved plants like rotala will also help protect fry.
The betta will certainly act as population control for the guppy fry. Do you plan on having fancy guppies with the long flowy tails? If so, the betta may get territorial and seriously beat up on the male and perhaps even the female guppies, resulting in torn fins all over. Unless you get a particularly placid betta, there could be carnage. Also, the betta will certainly eat any shrimp in the tank. I put a stowaway ghost shrimp in a tank with a female betta once, and it was amazing and viscious watching her stalk and repeatedly attack the poor shrimp. Ottos are a great choice for a ten gallon, IMO, and will be ignored by pretty much everybody.
