I was thinking fortnightly to start with, to keep people up to speed with the formation of WMUK2 and so that the Board could ask questions of the community beyond this mailing list fairly easily. After that, it would depend on how much actually happens with WMUK as to how often we want to send around a newsletter.
I think things are moving too quickly for that at the moment. The board are having weekly meetings for a reason. If a newsletter is sent out every 2 weeks and then it takes about a week for responses to come in, that means consultation could take up to 3 weeks. That's not practical at this stage.
Technically, I was thinking that we'd set up a page on Meta which would hold the newsletter (probably using a formatted template), then use a bot to push a link to that page to everyone subscribed. Sending around an email with this link would also be do-able. The alternative is something like WP Greater Manchester's newsletter on the Signpost Spamlist, where a copy is pasted onto the subscriber's talk page. That makes it a bit more challenging to put it in an email. Which would people prefer?
I would prefer actually including the newsletter in peoples talk pages (or, at least, a contents page, like signpost does, depends how long it is). People are more likely to read it that way.
We may eventually want a snail mail version, but I would be surprised if many people wanted to subscribe to it - if you know Wikipedia, then you have internet access, as a rule.
I wouldn't have it as a subscription thing, I'd send it to all members. It's nice to receive something physical for your membership fee. Obviously, a snail mail version would be less frequent, quarterly tops.