Hey, you want a turtle, and that's your final decision, no stopping you, then by all means, get one.
However, I'm gonna tell you straight up that turtles are EXPENSIVE. They don't need huge tank adjustments and upgrades very often, like, at the most annually, but those adjustments/upgrades are never cheap. Especially if you wanna go all out and make a zoo in your tank. (Some people, like me, actually do this). Unless you look in the cheapest places, I guarantee you will spend between 500 to 1,000 dollars on your turtle by the time they reach adulthood, and maybe even more.
Turtles should have the following things (At least, I think they should):
1. Basking ramp. It can be a floating piece of cork bark, a floating log, one of those commercial ramps that suction cups to a wall, or the turtle tank topper.
2. Water heater, heat bulb, UV bulb. Don't get Repti-sun bulbs that are 10.0, since they cause eye problems. 5.0 is much better.
3. Plants. They can live without them, but turtles love to have artificial plants to hide within.
4. No substrate, unless it is fine grain sand. Turtles are known to eat gravel and suffer severe internal injuries because of it.
5. Flat river rocks. You don't have to buy these, you can pull them out of a river bed and soak them in bleach, then soak them in water until they no longer smell like bleach.
If you want your turtle to be very social and comfortable with being handle by you, and your dad, I suggest getting one between two and four inches. There are strict laws throughout the United States about keeping turtles under four inches, so, check out where you live and what you can and cannot do. I had two inch turtles (they were stolen from me. I'm working on getting my girls back) and I was going to start using them for educational purposes at the school I work in. (Just know that little kids can't hold little turtles. Besides everyone's salmonella paranoia, little kids are rough boogers). You can properly socialize a turtle larger than four inches, but it requires a great deal of patience and takes a very long time, as well as a crapload of knowledge about reptiles. (Something that I don't have, so, don't ask me for details)
Just get one turtle, okay? RES don't get along well when they live together. RES are very strong, and when they get older they can really kick the crap out of each other. They act differently to tank changes when they live together, too. If I change something and my girls don't like it, they abuse it, or they nip at each other a few times.
I would really like to know why such expensive, and at times aggressive animals became popular pets. It's the same way with those spotted cat breeds, like Savannas and Egyptian Maus. I have a Mau and he is a nasty em-effer when he wants to be.
I buy supplies usually from this website:
http://www.petdiscounters.com
I like that site a lot, but read the product descriptions very carefully. Their turtle supplies section is the largest, as far as I can tell. Their plants are lovely, their ramps are cool, and they have some great bulbs and lamps. Cheap too.