Memberships can be of use as a vehicle for keeping out pissheads/trouble - ie 'sorry strict policy you can't come in without one' to anyone you don't like the look of.
Be a little wary of getting too 'something for everyone' as you'll end up inundated with people wanting to hear Babylove etc if you're not careful which will tend to drive away those with a more serious passion for the music.
Where in SW Scotland - we're in Carlisle. Keep the venue small (at least initially) as a packed small venue is much, much better than a half empty medium-large venue and of course the overheads are less precarious, attached parking is also very useful as people get nervous leaving their cars late in the evening somewhere they don't know.
Best of luck.
Dx