We usually have 5-6 weeks between auditions and opening night.  Most of out rehearsals run Sunday through Thursday.  This gives us 20-24 rehearsals before opening.  We may give a musical a few extra weeks.

We average 17-20 rehearsals for plays, another week for musicals. Ours are 3X wk. for 3 hours. It's nice if you can make a schedule that doesn't require everyone to be there all of the time. Keeps people from sitting around when not on stage and actors appreciate it.

 IMHO once a week is not enough to get it done, everybody sort of loses focus after a week and you end up going over and over and over the same stuff.

 For something like Xmas Carol, almost anywhere could be a rehearsal space. I have a coffee shop I use when they are closed. A local Christian School in the evening.  A city park with a covered area. It all works, and can be a wonderful growing experience for the actors (and directors).  Look around, there are spaces to use. Be creative.

I've done twice a week for the last two one-acts I've directed.  It worked out really well because things stayed fresh enough, and no one got burnt out.

But I can't imagine that I'd be able to keep the momentum going rehearsing twice a week for a full-length.  Especially if the cast was larger than 4 or 5.