Hmm.. firstly, make sure your tank is setup and fully cycled (could take 3-6 weeks) before adding fish.
Do you know if the guppies are all males? Could run into some aggression issues depending on the groups gender composition. A small group of males will typically be peaceful, but if you notice any of the smaller males getting picked on best to take corrective action. If you get both genders, try to have at least 2 females per male minimum, 3 would be better (or else the females will literally be chased to death for mating purposes). Also, females get bigger than males, so having a mix will reduce your ability to add more fish. Endlers guppies (all males) would prob. help you here since they don't get as big as the fancy guppy breeds.
In the wild guppy's spend most of their time and energy searching for food, so out of survival necessity they don't generally pick on each other how they will in an aquarium - since most of their time/energy is spent getting the daily food intake they need. In an aquarium, they have more time/energy to kill. Hence why a small group of males just need monitored.
Guppies almost help "some" with algae control, but will still need a proper diet of flakes/brine shrimp/veggie pellets/ bloodworms etc. Etc. Just try to mix their food up time to time, you'll notice their colors come out more too with a proper diet.
Since they do help some with algae control in the mid/top lvl's, and since you don't have a whole ton of room extra in your tank without overstocking, maybe consider some amano shrimp or nerite snails to help with cleanup? As a couple nerites won't overly affect your biome, and they live fine in freshwater but only breed in saltwater (if I remember right) so you don't have to worry about them repopulating, but they'll help with algae in the bottom lvl's. Snails like to climb out of the water a little bit from time to time too, so if you go with snails get a secured lid and try to give them an inch or 2 of roaming spacee above the waterline.
Shrimp could also be a big help to keep the bottom cleaned up, like uneaten flakes etc., and not overload your biome too much - but they reproduce like mad in the right conditions, and you'll want to give them plenty of cover regardless too. Java moss would help a lot.
Either way, if you end up slightly overstocking your 10 gallon by a tiny bit, double up your water changes from what you had planned and you should be fine (as long as it's not SUPER overstocked and your first cycle is over, just keep those water changes coming. Solid biological filtration would be key here.)
Hope this helps.
