Hello and welcome.
I too have an iMac (21.5-inch, Late 2009), running macOS High Sierra 10.13.6. It won't update to the very latest versions of macOS and some applications, but most are new enough.
Yes, that iMac is a good choice, but if you budget can handle it, moving up to the $1499 model gains you a few things:
-A better 6-core processor
-Fusion Drive instead of the standard 5400-rpm hard drive. The SSD option is even better
-Dedicated Radeon graphics
NOTE: RAM is not user-upgradeable after purchase, so keep that in mind.
The standard 5400-rpm hard drive is very sluggish. iMacs used to have 3.5" 7200-rpm desktop hard drives in them, but Apple switched them to 2.5" 5400-rpm laptop drives The Fusion Drive is faster, but the SSD portion of it is smaller than in previous models. Personally, I would go for an SSD - even though it may be small at 256 GB for the base size, it is so much faster than both of the other choices. If you need more storage, you can always add an external Thunderbolt drive with SSD to startup from or store large files on.
You could actually consider the new MacBook Air $1299 model, as it has a quad-core processor, 8 GB RAM, and 512 GB SSD storage. You could add an external monitor for home use, and have the ability to take it on the go with you.
Hope that helps and let us know if you have additional questions.
C