Single channel is correct because you aren't running it in Dual Channel which requires two sticks of equal size, density, manufacturer, they have to match EXACTLY is what I'm saying. Even then you have to put them in the specified slots that your mobo's manual says will allow the RAM to run in dual channel. So if you have 2x512 then you need to find out which two slots give you dual channel.
The frequency of your RAM is also correct....200MHz is where it should be.
DDR stands for DUAL data rate, so when you see that 200 you gotta multiply it by 2
200x2 = DDR400
Everythings in order so you're good to go.
how long am I able to overclock
doesn't really make sense, if you're asking how long will the RAM last then that's anyones guess. Every system and RAM chip differs from the next so there is no simple guideline to follow like that.
Same applies to your second question....there is no timer for when you have to stop OC'ing...
Whenever your computer crashed =D
EDIT: BTW OC'ing the RAM is a lot different from OC'ing the CPU so I hope you have a decent knowledge in both.
Unless you have really good high performance RAM chips I wouldn't expect a huge increase in RAM performance.
Also remember it's pointless to have your RAM running at 210MHz or DDR420 if you have your CPU FSB at 200....you'd just be creating a bottleneck and if they can't communicate at the same speed then it's worthless.
As it is, your CPU and RAM aren't on a 1:1 ratio which is what it should say in CPU-Z but yours says CPU/11