Guppies & Tetras
If you are planning to keep fish as a hobby and you can afford a 20-gallon tank then I would upgrade to one early on. It is easier in many ways to have a larger tank. The only 10-gallon tanks I use are quarantine, grow-out, or breeding tanks.
Neon Tetras & Guppies are not the best tankmates. Guppies need hard, alkaline water (7.8 or above) while Neon Tetras need softer, acidic water (the closer to 4 you can get the better). Guppies are livebearers & livebearers have a life cycle which includes a saltwater phase & the ph of the ocean is around 8).
If you like the way Guppies look you may wish to consider Endlers or Guppy/Endler hybrids. Endlers are trickier to breed, however, that is a good thing if you are not planning on breeding your fish. Endlers are as beautiful as Guppies without all the inherent genetic problems Guppies have. Sadly, so many people buy them, allow them to breed in an uncontrolled manner & then just toss them. They have become throwaway fish.
I wish you a lot of good times with your fish & I think it's WONDERFUL that you care enough about them to make sure you are giving them a good home and want to meet their individual needs so they will be happy & healthy. Too many people think only about what their fish will LOOK like and what is prettiest with what, not thinking about the conditions which are needed by the individual breed of fish.
Stay safe & well in these unsettling times.
Sláinte
Adi