Ex's house can easily cope with 40-50 people (including DHs and DCs) as long as everyone was careful with the antiques (think National Trust but more homely). So probably 10-12 considerate families tops, depending on the number of manic toddlers included in that. As we have all met on the internet, there would need to a bit of sensible security stuff, such as me knowing everyone's names and addresses, for obvious reasons, but nothing too onerous or intrusive.
On a sunny day it would be even better because he has an acre of walled garden, well suited to kids running around or whatever.
College can cope with any number of random people, and the catering is very tasty and good value. It also has plenty of space outside and lots more toilets.