"I'd really like to start a night in Liverpool or Manchester that played the best of the past twenty years or so of 4/4 stuff (house, techno, electro, etc) with a bit of flair and imagination. As opposed to just playing the latest releases in a narrowly defined genre or devolving into the sloppy eclecticism that marrs so many club nights. I've got the decks, the records, a good rig built by a mate with a degree in audio engineering, mates that can mix, a bit of cash to put into it...but I'm not really sure how to go about promoting it."
I don't really see why eclecticism has to be sloppy but never mind...
Anyway, from what you've said above you haven't mentioned a venue and to me that's really important. For our nights we always try and use a different venue to keep it interesting - the problem every time is finding a new and good one. However, even if you're not going to do that (perhaps especially) you need to find somewhere that's suited to your needs. I don't know what the situation is in Liverpool or Manchester but for me you need to think about how late it's open - I think a night becomes much more of an event if it goes on until the morning and if that's what you want then that immediately restricts your choice.
Also you need to think of the soundsystem (presumably you will have to use theirs rather than putting in your mate's rig) and the general vibe of the place but I'm sure you know that.
For promotion, we've always done a mixture of posting it on chatboards, mailing friends and their friends and stuff and loads of flyers. For me, flyers can be good as long as they are good flyers, if they are not then they may do more harm than good. We always hand out loads in all the places near the venue every day of the week for - maybe - two weeks before the end. Chuck 'em on tables in bars etc the ones that don't get picked up will get thrown away but it doesn't matter because you will put some more there the next day.
If there are local listing mags then try and get in there as well obviously.
Collect the email addresses of people who come and try and build up a mailing list, obviously it's very important that you get your friends to come for the first few times but you can't expect them to give up every first Friday of the month or whatever so you need to keep getting new people coming.
Regarding money, it depends what the deal with the venue is, normally you pay to hire it (sometimes it's free, sometimes there is a deposit) and you take the door and they get the drinks money. There are other arrangements but that's a standard one. What we normally do is then add up the costs of the venue, the flyers, any guests/bands etc and then maybe add on a hundred pounds or so (to give you some leeway) and then divide that number by the venue capacity and that's your door price (the lower the better of course). In other words, if it's totally full you will make a ton - unless there are any unforeseen costs. The last night we did we had to change the venue because the original one got raided, the new venue was £200 more expensive which completely wiped out the excess, that meant that after literally months of work and stress I ended up with a grand profit of £20 but everyone had a good time so it was worth it.
I would say don't be too ambitious on your first night. The worst thing that happened to us was when there was a fire on the day of our party and the police roped off the street where it was supposed to happen. We had to move at the last minute to another venue where we couldn't charge on the door and, as we'd brought a guy down from Chester and a girl from Edinburgh we ended up losing more than £600. That's not too bad though, some guys I kinda know did a night recently where they flew someone over from (I think) Israel and ended up losing about four or five grand between them. Nothing even scuppered that, just not enough people turned up.
About guest djs, that's your call I guess. If there is someone who you want to play and will bring some people then maybe do it. On the other hand, presumably you are doing the night because you want to have some fun spinning records so you don't want to have too many guests. It's no fun if you spend months promoting something and then on the night you're on the door and it runs behind and you don't even get to play.
What can be good though is if you can team up with like-minded nights then that can be very nice, they play at yours, you play at theirs, they advertise yours and vice versa.
Also, live acts are something that people seem to like. Personally I can usually take it or leave it but it's surprising how often you see people asking at the doors of clubs if there are any bands on - might be something you want to think about anyway, I don't know.
Oh well, good luck, let us know how it goes.