I have a Macbook Air -13, i7 8GB ram with Solus Plasma on for testing and it works fine for browsing and editing a few docs in onlyoffice.
XFCE is known to be light on resource usage in case Plasma does not work or is not of interest to you.
Installing Solus is just a matter of downloading a ISO and creating a USB with it, boot from it and when you get to the desktop select install and follow the instructions from there.
How to get the Broadcom wifi to work see here
Regardless you can’t go wrong with Ubuntu either in my opinion if that feels more appropriate for you.
The best option is to try out a few alternatives to see which feels right for you at this moment and start there.
Best of luck!
