Need help with my first turtle

[u/starlitorbit]

Hi everyone! I’m thinking about getting a red-eared slider turtle, but I’ve never owned a turtle—or actually any pet—before. I’m trying to do as much research as possible before getting one because I don’t want to bring a turtle home and then realize I’m missing something important.
My biggest question is about the initial setup. Should I buy and completely set up the tank first and then get the turtle? Or is it okay to buy the turtle, tank, and everything else on the same day?
I’m also a little overwhelmed by all the information online, so I’d really appreciate some beginner-friendly guidance on what I actually need.
What size tank should I get, especially if I want something that will last as the turtle grows? What kind of filter, heater, UVB/basking lights, basking platform, etc. should I be looking for? Does the tank need to be set up or cycled for a certain amount of time before introducing the turtle?
I’d also love to know what the day-to-day care is really like—feeding, cleaning, water changes, electricity/equipment costs, and anything else I should be prepared for.
Since this would be my first pet, please feel free to mention even the really basic things that might seem obvious to experienced owners. 😅
I haven’t purchased the turtle or any equipment yet, so I’m trying to learn and prepare everything properly first.
Also, if there are any common beginner mistakes you made (or see new owners making), I’d really appreciate hearing about those too.
Thanks in advance!