Red-ear Sliders are a good starter turtle in the sense that they're virtually bullet proof. They are very, very hardy as far as turtles are concerned. However, they ARE a lot of work.
A basic rule of thumb for enclosure size is 10 gallons
of water to every 1" of turtle. So you're looking at a 100 gallon or larger aquarium for a female, and at least a 75 gallon for a male, and that's not counting if you have an actual "land" section (as opposed to a floating or above tank basking area). It should also be noted that they grow FAST... I have an acquaintance who has a good-sized female RES. Despite an absolutely awful care regiment and tiny tank (no UVB, heat light on only sometimes, crammed in a half-filled 20 tall with 2 other turtles... Luckily he's seen the error of his ways and started giving better care), the big gal was 8" or so by about 2 years of age. Imagine how big she'd be already if she'd been raised right!
As far as land, you can go with a basking platform that floats in the water or sits above the tank, and therefore avoid taking up precious swimming room. The above the tank platforms are especially nifty, as you can build it to your specifications and they won't sink under the weight of an especially heavy turtle.
With diet, they're a bit like beardies in that they start out mostly carnivorous and, by the time they reach adulthood, evolve to be largely herbivorous. You can use a couple high quality commercial foods as staples, with good greens, bugs, and thiaminase-free fish to supplement (NO GOLDFISH!!! I can't stress this enough--goldfish are CRAP, awful feeders!) Also, be careful not to overdo it with protein. Too much protein ("meat") can cause pyramiding in aquatic turtles.
There are a couple other species I'd recommend before a RES, who stay much smaller but are just as hardy. The first that comes to mind for me is Mississippi Map Turtle... These guys are pretty tough, too (to give you an idea--the 2 unfortunates who grew up with my acquaintance's RES are Mississippi Maps). The females can still get to a pretty good size (6-10"), but the males are generally 3-5", so they're overall a smaller species than RES. Smaller, of course, means you don't have to dedicate as huge a space (though, they'll still use a giant aquarium if you give them one!). They're a bit more carnivorous than RES.
http://austinsturtlepage.com/ is a great resource, with care sheets on several different species including RES and Maps. They also have a great forum at
http://www.turtleforum.com/.
http://redearslider.com/ is a great care website geared specifically toward RES.
I know this response is a few weeks late, but I hope it's helpful to you nonetheless.