Hi maimuki, the minimum number of tables for M Hotel is as follows:
Weekday Min 20 tables Max 32 tables
Weekend Min 25 tables Max 32 tables
This is true for both the Anson Room and the Banquet Suite packages. For more details of the pricing and all, you can check out the PDF files that are posted here >>
http://www.singaporebrides.com/hotels/m_hotel/
As for the food I can't really comment since I have not tried their food before at wedding dinners so hopefully someone else can share or maybe try reading through the forum for more feedback. But I don't seemed to read much really bad feedback? That's the feeling I got after reading some pages here. As for the ambience, I must say my hubby and I quite like it after making a visit to M Hotel to see a wedding setup the day we met Eugene for an appointment. We both feel the best fit is maybe around 25-27 tables at max for more comfortable walking space and all.
Maybe I can send you some photos of the theme of the ballroom when I get back home 'cos we went to the previous wedding show and took some photos of the theme setup. Alternatively, you can make an appointment with one of the M Hotel wedding co-ordinator to best find out and get a feel of the place. Thought that might be the best way to know 'bout the venue.
Hope this helps!