Guppies are called 'millions fish' for a reason. If you add plants to the tank (either real or fake) and add a dark substrate (ideally a mixed bag of browns, blacks, and reds) and feed the tank daily you'll have more fish than you know what to do with in a couple months.
I started with 3 guppies a little over a year ago, and now have given away about 50, and have a chronically overstocked 10 gallon with over 80 guppies in it. (water parameters are fine, but kids, don't try this at home. I've been keeping fish for over a decade.)
Once the density got that high, I started fasting the fish two days a week so they'd slow down reproduction and hunt down their young. My tanks are all well planted, and that's my show tank.