I recommend you start small. maybe a 2.5 gallon tank. this way you will spend less and understand the process.
2 gallons is much ceheaper to stock than a 10 gallon.
Stem plants you can buy are anacharis, water wisteria, cabomba, naja grass...
one or two bunches can fill up a two gallon. when you plant them. simply inset it the right way up into the substrate. if the stem plant is longer than the tank, simply cut it in half and plant both halves.
floater arent really sold in petshops. howeer water wisteria an anacharis do very well left floating, so these can be a substitute.