a. How many regulars you know that you dance with.
Hard call, but counting all the milongas I attend each week, in the neighborhood of 40-45 each week and maybe that many more (another 40-45) at least a couple of times per year.
b. How many regulars you are familiar with whether you dance with them or not.
I'd call the 80-90 people I dance with at least sometimes "half the regulars I'm familiar with," so while it's an estimate based on an estimate based on an estimate, I'd claim familiarity with 160-180 people. I count ~200 tangueras as Facebook friends, and they're not all the tangueras I know, nor are they all the tangueras I dance with.
c. How many of your dances are using cabaceo with people you don’t regularly dance with. How many by asking verbally or walkaceo.
If it's people I
don't regularly dance with, it's 100% cabeceo. I only invite a person other ways if I know them at least moderately well.
d. If person you know is at the opposite end of the room, what do you do to ask them.
Cabeceo, unless I reserved a tanda. I reserve a lot of specific tandas (first/next/last vals/milonga/D'Arienzo tango/whatever) for friends, either before the event or when I pass someone during it.
e. How many non-regulars, non-familiar do you dance with on an average night.
Maybe one or two. Sometimes none . . . If even half my regulars for the week are present (say, 20 people) and I'm going to be there for 14-16 tandas, there won't be room on my dance card for new additions.
f. What typical size or number of people at the milonga.
Super-variable! I attend 3-5 milongas a week – not always the same 3-5 – and attendance varies with weather, DJ, competition, holidays, etc. I've seen as low as 30 and as high as 120 on typical weeks, and sad milongas with 20 people during snowstorms and crazy ones with 300+ people for special events. I guess I'd peg 50-60 as "average," but it isn't a stable average.
g. What is the gender ratio.
Most often between 3:2 and 2:1 F:M. There are times when it's briefly 5:4 M:F near the start of the event; I get the impression that men show up earlier. I've never seen an event that stayed that way or worse. I've seen quite a few where it was 3:1 F:M, and I remember one where I was one of just two men for the first hour, and there were about 20 women.
So, a typical milonga for me might have 60 people in the form of 36 women and 24 men, I might know 18 of the women, regularly dance with 9 of them, and invite a few friends twice and a few newcomers once. I'll go to 3-5 like that a week, and it's quite possible that I'll see totally different crowds at each one, so it's plausible that's 27-45 different regulars a week. In practice there's a little overlap, but also in practice there are more people than that unstable average, and most of the "more people" are women . . . the busy places with 3:1 F:M tend to look like the less busy places with 2:1 F:M except with 50% more women.