I would get a clear 5g plastic tub (tote) with a very thin layer of sand. (I mean really thin, so they can’t bury themselves completely) Also make sure to get a sponge filter and heater.
Having a sand-less QT tank really isn’t fair to them, because they require sand.
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I agree with
@GuppyBreeder180604 on the numbers. 6 is the number of fish we usually recommend for beginners, but I always stock 8+. I learned how important this was, especially after getting my 8 False Julii Corydoras. When I just had 4, they sort of split off into tiny groups. When I added the other 4 however, they all started swimming together and overall seemed more happy.