I actually had the E4200. Nice looking, and worked better than it's predecessor. For a while my Linksys devices would just degrade very quickly, first with constant reboots needed to keep throughput working, then eventually throughput just dropped down to about 1 Mbps. It was ridiculous.
Anyway, on any dual-band router, including the E4200, you can name your bands separately. For me I named them after my pets. That's irrelevant but for this purpose it made sense. I named my 2.4 GHz network "Tigger" which is my older pet, and my 5 GHz network "Autumn" which is my younger pet that will probably live a lot longer and not be weighed down by the problems of her age like Tigger. It's all very poetic, for a pet owning geek, I guess.
Anyway, any devices that is dual-band can see both of them, so I always have those jump on the Autumn (5 GHz) network. Anything that's single-band can only see the Tigger SSID (2.4 GHz). You can leave them named the same, but this leaves it up to the client and AP to decide what radio it ends up using. I liked knowing that I was getting the advantage of my 802.11a/n radio's throughput and low-noise connection. And since 2.4 GHz travels further, when I'm out in the yard or something I can still connect to that with decent strength if 5 GHz is weak that far out.
One of the biggest benefit of this setup is, since each radio is basically "hub" technology (half-duplex, single-bus behavior), I get much better performance in both bands by dividing up the collision domains like that.
As for 802.11n, this is available in both bands, like you pointed out, but by doing the multi-SSID approach, you can decide which band you use your n-device on. For me I decided to disable n on my 2.4 band because I didn't want it to jump up to the 40 Hz window, stomping out 2 of the 3 non-overlapping channels in 2.4 GHz range. On the Linksys you can control this though. Also, if you can disable B w/o disabling G, you should. If there is a devices connected to your 2.4 radio with 802.11b, it will bring all other devices to their knees (B-level throughput) while it's connected. For my 5 GHz radio, I forced N-only so that I know I get the full throughput, and I know that all of my 5 GHz devices are 802.11n capable. This has the added benefit of not allowing devices on that will pull your N speeds down to A speeds.
There's a lot of fun to be had in planning out your wireless network. Lots of manipulation you can do, even on home routers, to get the performance you want. If you really want to have control of what's going on around you, and have lots of money, get yourself a Xirrus Array (XR-1000 is plenty for home use). You can play terrible tricks on your neighbors with deauths and blasting out channels at high RSSI. I don't recommend this, of course.
You might consider looking at DD-WRT for your E4200 if you want to add a ton of cool features that you can't normally get w/o expensive enterprise gear. VLAN tagging, SIP, charge for hotspot, guest network (most have this anyway now), etc....