There is definitely an Inyan to serve Fleishigs l’Chatchilah at any Se’udas Mitzvah, including a Bris. As a matter of fact, the overwhelming majority of Brisim here in Eretz Yisrael are catered Fleishig affairs, usually quite early in the morning. For reasons mentioned already, in CHU”L many people prefer Milchigs. This may be justified in Poskim, but it is definitely not the Pashtus.
Regarding the Milchigs and Fleishigs together – as many have mentioned, very problematic Halachically, unless there is a Heker between those eating one gender and those eating the other.