I have a MacBook Pro late 2013 with 16 GB of memory and 1 TB of flash storage. I also have an external Apple LED Cinema Display. I am currently running macOS Sierra 10.12.6.
I do Hybrid App (i.e., with Cordova plugins) development on the host O/S (macOS). So I can run emulators, etc.
I do PWA (i.e., without Cordova plugins) development on the host O/S or on a VM running in VirtualBox.
An i5 with 8 GB RAM should be enough. Just make sure you choose any Mac with more than 128 GB of drive space, otherwise you’ll be struggling to install XCode, your IDE, and all Ionic dependencies.