In this comparison of the Makita, Dewalt, and spindle, Eric found the spindle much quieter, but significantly underperformed the routers. And this was a 500 watt spindle, which is not the lowest you will find.
you shouldn’t go quite larger than 60x60cm and 81mm height
I see people posting on the forum about MPCNC machines significantly bigger than these numbers all the time. You just need to understand that you pay a performance penalty (especially in the Z height) if you go bigger.
While it varies a bit based on your choices and the axis, you need approximately 380mm beyond the working area X and Y for the total footprint.
How much difference an enclosure makes will depend on how you construct it. My enclosure made a substantial difference, but I found during the summer it also held in a lot of heat in an already hotish room. Plus as Jeff mentions, my enclosure does nothing to quiet the vacuum when I use one.
My table is about 120x85cm
If you need it to fit on this table with nothing hanging over, your max size is about 830mm x 425mm.