The Seder will be on the 18th as for corporate worship well there will be a Pastor and about 60 people there. That could be considered corporate worship even if not everyone is a member of the church. (And no it wasn't/won't be on the Lord's day)

Number 3 is the sticking point for me. I know it is popular among some "evangelicals" to do Messianic Seders so to get in touch with their Old Testament side and experience the Jewish "roots". But I don't see the point.

Yes I do think Col. 2:16-17 applies I'm not going to his pastor and say that he's falling into Judaism cause I know it isn't true however I do think there might be a streak of Theonomy in this but I can't say for sure.

Peter

If you believe what you like in the gospels, and reject what you don't like, it is not the gospel you believe, but yourself. Augustine of Hippo