Usually, not always...but most of the pet shop will give you all the MTS you want since they are pest snails. I personally like them and they all have jobs in my soil based planted tanks.
Since you are in Texas, you have several aquarium clubs and you could also check that out for both snails and plants.
As for the sand, I have used that to cap my soil for my natural planted tanks and it has worked well for me. The dark colored sand can really help the Betta color pop.
I use half as much sand to cap my soil in my NPT's.
Your plant choices look good for a soil based NPT.
I don't use filters in my smaller soil based tanks-I let the plants function as the filtration/biofilter. Sometimes I might use a filter for the first couple of months until the soil matures-then I remove it-since its not really needed-provided that you have enough of the right species of plants in active growth. Floating plants-like water lettuce are also helpful especially in your soil based systems and recommended.
Some of the Long fin males can have fin issues with water movement-especially in the smaller tanks. IMO/E-filters are optional with this species and with live active growing plants that will function as the filter to help with water quality.
Proper color temp lights are the most important with planted tanks-regardless if it is a NPT soil based or regular inert substrate like sand or gravel.
What kind of soil are you going to use under your sand, what kind of lights, age of bulbs, kelvin, watts and planned photoperiod.
If you only plan to use that sand and not use any soil-you don't really need trumpet snails, however, I wouldn't use more than 2 inch of the sand or place a wide item on top of it-bury the base to help prevent anaerobic issues. Once the stem plants start to grow-their roots will help pull oxygen into the sand to prevent anaerobic problems. Adding shrimp will be fine, however, unless they have lots of places to hide they might end up as a snack-Some Betta tolerate them better than others. Adding snails are fine too IMO/E and this will complete you little ecosystem.
Look forward to pics....