The article I linked to actually covers a lot of that
But anyways, I would just get a turtle food like ReptoMin's. As strange as it sounds (with the crappy looking ingredients), it IS a balanced diet and turtles do very well on it. While the foods you listed are fine (although I'd skip the beef and chicken), I highly doubt that anyone is going to keep up with that diet when they take the turtle home
. Suggesting that they feed those foods as treats/supplements would be great but I would recommend that they feed a pellet-type food as a staple. Even if they tried feeding a homemade diet like that, it would be easy to get lazy/cheap and end up feeding only a few of those things--leading to deficiencies. With a good staple pellet, you don't need to worry about adding vitamins or anything.
Also, most turtles won't touch vegetables, at least not without a fight
. Adult turtles will nibble on greens but it's hard to convince most turtles to try veggies. You're right, though, babies don't eat much vegetable matter at all while the adults do.
There's no reason to add supplements when the turtle is on a pelleted diet (since those things are added). Most turtles, from what I've seen, ignore cuttlebone or try to eat the whole thing.
There's no need to heat the water unless the house is REALLY cold. In fact, heating the water can sometimes be a bad thing--they won't feel a need to bask. RES are not tropical turtles (they live in NY, in fact--they're invasive, but yeah...). What's more important is a good basking spot
I have an actual reptile basking bulb but it was cheap, like $6 or something. Don't bother with an expensive one. Once I used a regular incandescent fishtank bulb for a few days (other bulb burnt out) and that worked fine (just not as hot).
My turtle won't bask on floating "island" type basking spots. If the turtle is the same way, find a way to anchor the basking spot or use a large rock instead (I did both and my turtle uses the island as a cave for sleeping, haha).
The only really expensive part is going to be the UVB bulbs. They're going to need to remember to replace them, even if they "look" fine.