Here is a link to a pretty good starter kit. It’s 20 gallons so your RES will outgrow it in about a year.
Tetra Aquatic Turtle Deluxe Kit 20 Gallons, aquarium With Filter And Heating Lamps, 30 IN (NV33230) https://www.amazon.com/dp/B075MKTGJM/ref=cm_sw_r_cp_api_i_sQXoFbRAXKNG6
smole turtle. Get a really good starter setup. Something like this: https://www.amazon.com/dp/B075MKTGJM as a basis. You can find very nice used turtle kits online.
You can get by with used and a smaller tank for now. However; you need to identify your turtle to know how big they will get and how big a tank you will need in the future (It could be 100 gallons or more).
My thoughts though lie with how did you acquire this turtle?
We had pebbles at the bottom but they were larger and I don't think the turtle would have been able to eat them being so small. And I had read multiple things saying that the pebbles were okay but to avoid using sand. Is that not correct? As far as the water level we would keep it above the minimum line for the filter but not so high that the turtle couldn't get to the basking dock area. We also had some artificial plants in there that the turtle liked to swim up and rest on with its head out. The Amazon link below is the tank that we got and the picture they use it where we would typically have the water level.
I purchased this tank along with the additional supplies: https://www.amazon.com/Tetra-Deluxe-Aquatic-20-Gallon-12-Inches/dp/B075MKTGJM/ref=sr_1_11?dchild=1&keywords=20+gallon+tank&qid=1599723946&sr=8-11
I also have a water heater coming in as well!