I’d argue that moving your Roon core from dedicated hardware to a shared use machine is not simplifying your Roon setup, rather it’s making it more complicated. Dedicated hardware is, generally, always going to be more reliable.
Given you don’t want to spend any $$, and assuming the laptop is running the Roon core fine, I would:
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stick your little Roon core laptop somewhere that you don’t have to look at it - e.g. in a cupboard connected to your home router/switch via ethernet and set the laptop to ‘always on’ with the lid shut.
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Use the Squeezebox as the Roon endpoint connected to your stereo as planned.
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Install Roon on your mac as client/remote only so you can control Roon from there, as well as use it as an endpoint (you can listen to music coming out of your Mac, nicely in sync with your stereo - yay!)
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Install the Roon app on any other devices (phone, tablets) you have to use as remotes.
If you are struggling for storage on the laptop a small 2.5in external HDD will need no external power to run off the laptop - 1TB is about USD$50.
And if you need to do anything to the laptop, connect to it via RDP from the Mac and you’ll never even need to get it out of the cupboard (my Roon core is running on a ex-lease desktop in the basement that I picked up cheap - I haven’t been down there for ages).