Which 13" MacBook Pro 2011 is right for me?
I've ordered the cheapest 13" as my first mac.
I already have a 80 GB SSD which I will put in it immediately when it arrives. An SSD is beneficial to about everything you can do on your mac because the hard disk is usually the performance bottleneck.

Don't worry about the screen size and resolution if you'll hook it up to an external monitor anyway. I've played around with a 13" a lot this week and the screen size and resolution are fine for normal pc usage.

I would not pay extra for the upgraded CPU.
Remember that the cheapest 13" has about the same cpu speed as the previous generation's 17" flagship! (see benchmarks posted below)

So either way I would go with the cheapest version.
If you are unable/unwilling to open up your mac yourself I would take the SSD option. You can always get a nice little external HD with 1TB disk space for not much money, if you run out of SSD space. 

Here are CPU benchmarks: