Don’t cheap out on a NAS, I got an entry level Synology when I first started it was great for learning but was quite slow. I needed to sell that and buy a more powerful model to get one that could run Docker. I went for 716+ which I bought used off eBay and works well for me, the difference in speed is night and day. Ram can be upgraded onboard if required. Good luck 👍
The 220+ was the first model I had, I found this slow and didn’t natively support docker as part of the package manager. Docker compatibility should be a priority when buying if delving into some setups mentioned here it just makes everything so much more convenient. The 16 series model is expensive to buy new, I picked mine up used from eBay from someone who was upgrading to a newer model. You can Google Docker compatibility for Synology models and get a list of models that work with it and narrow your choices down to these.