I plan on keeping the small tank around as a hospital or quarantine tank
I was going to say that the five gallon will make a perfect quarantine tank!
Or a nursery, since you have female guppies... just a warning, guppies are also known as "millionfish" for good reason! I've been trying to stop breeding them for months now, thought I'd sold all of my viable females and fry, and yet another huge batch of fry has recently appeared...
So it may turn out to be a useful nursery/grow out tank for you! Always handy to have a spare tank in any case.
How would you feel about adding more live plants? I noticed you have a couple already, that's good! Those ones you have will grow better if you remove them from the pot. Just loosten the plastic pot, then gently peel away the rockwall (the beige, fluffy stuff all around the roots) in small strips, gently, trying not to damage the roots too much. That rockwall is just a growing medium, but it also kinda restricts the roots from really spreading out and letting the plant establish itself. Once you've freed the roots, can replant the plants directly in the gravel.
Depending on which plants you have, they'd benefit from either root tab fertilisers, or a liquid fertiliser added to the tank now and then. (some plants get most of their nutrition from the roots, others from the water column).
Floating plants are one of the best you can get. Fish are very vulnerable to predators, both birds and other animals from above the water, and predators below. So a big open space and having nowhere to hide is very stressful for them. Lots of live plants improve your water quality, since they take up the ammonia the fish produce, and make the fish feel much more comfortable. They interact with live plants in a way they just don't with fake ones. Floating plants are easy to grow, don't need any special care, are one of the best for sucking up ammonia, and make fish feel a lot safer from overhead predation. They help shield fish from bright tank lights too, since most are used to much dimmer lighting in their natural habitats.
If the plan is to breed the guppies, fry also tend to head to the surface, and they're safer from hungry adults if they have some floating plants to hide in
Nothing wrong with keeping the fake ones too, if you like them! As long as they're not a sharp, hard plastic, they shouldn't harm your fish. Can always kit it out with the fake decorations, then gradually add some more live plants as and when you find ones you like.
Edited because I do know the difference between their/they're/there.
