Which EMC do I have, 2210 or 2213?

Your system has a SATA II (3.0 Gb/s) interface. You'll need to review the spec sheet of the drive you are planning on using to see if it supports this speed.

You'll find two types of drives 'Fixed' and 'Auto Sense' a Fixed drive only supports one speed (only the one speed listed is what its designed for). An Auto Sense drive has added circuity to matchup with what the systems SATA port has (it will have multiple SATA speeds listed).

Given the age of your system I wouldn't invest too much into it. El Capitan OS-X 10.11.x is the highest you can run on this system. Apple no longer services the system and won't be offering security updates for El Capitan soon.

I would recommend maxing the memory (6 GB) and putting in a cheaper 3.5" SSHD which will get you the zip I think you're looking for. Here's one option: Seagate 3.5" FireCuda Note the interface supported line, this is an auto sense drive.

If you go with an Crucial SSD You'll also need an adapter frame to mount the smaller SSD. OWC 2.5" to 3.5" Drive adapter frame

Here is the IFIXIT guide you'll need to follow: iMac Intel 20" EMC 2133 and 2210 Hard Drive Replacement.