I tend to think that the first March announcement we get will be either: the return of Bill & Ted, the return of Jack (who was the first announcement of HHN 25), or the return of Terra Queen (whichever of those is coming this year).
As far as when the first HOUSE is announced, I think it will definitely be an IP instead of an original, as usual. Furthermore, a lot of the first house announcements are "series" IPs instead of movie IPs (Stranger Things 2x, AHS, TWD, etc.). So, I'm going out an a limb and predict that the first HOUSE announcement will be Haunting of Hill House (or whatever Netflix property they bring this year).