External display

I decided to settle for a 13" instead of 15" since the only thing I would get out of the 15 was a bigger and higher res screen (well the only thing that would be of much use to me), and I decided it wasn't worth the $600+ difference, and that if I was going to spend that much, I'd rather get a MBP 13 and iPad anyways.

So since I mostly am only on the computer when I'm at my desk, an external monitor makes since, and I can deal with the small screen size on the occasional times when I take the mac with me.

I have a few questions about external displays. If I get a 16:9 (1080p) display, while the mac is 16:10, will the screen still look normal? Will there be bars on it or will the image get stretched or anything? Cause it's a lot easier to find a 1080p screen than a 1200p, and I think they look better too.

Also, do I need any special cables to connect the screen? What is the standard cable used to connect to it?

And is there a noticeable lag when you use an external display? Idk why there would be but I just wanted to check. I know when I plug my computer into my TV via HDMI, there's like a half second lag sometimes.
Does it use any more system resources than using the built in screen? Like if I'm using all of the CPU, would it slow down at all when using an external display since it has to send the picture to another screen?

Sorry for all the questions, I just want to make sure there aren't any drawbacks to doing this

 

Yeah I know there are a ton of advantages to the 15", I just meant that I wouldn't really benefit from most of them very much for what I usually do, and that the screen size was the main factor in me wanting the 15".

Thanks for your help!