If you have more than one version installed do you need to keep choosing and also installing those module support builds each time ? I feel thats going to take up space fast
I don’t know what you mean about module support builds. But yes, multiple versions take up a lot of space, but they’re the only way to have multiple versions. 
Use Unity Hub to help keep them organized and automatically launch the right version for each project.
Yes, the support modules needed to support additional platforms are updated with the engine making it necessary to install them for each new release that needs support for those platforms.
There are no meaningful performance penalties for using low-cost high-capacity solid state drives making storage one of the least expensive aspects of game development. Plus it’s not like you will need that many releases installed at any one time. USB 3.0 flash drives have more than enough performance for Unity if you can’t easily upgrade your computer.
It is pretty normal to have multiple Unity releases installed. Older releases for supporting released or late in development games, recent release for a new project, maybe even a beta release for some experimentation with yet to be released functionality. Yes it uses more storage, but not that much unless you’re being extremely stingy with how much you’ll spend on disk space. An Intel 660P 1 Terabyte SSD sells for $100 USD right now.