Ahh...ok band demo to sell the band to club owners.
Been there, done that, and yeah, with the 3 piece band I played in.
My advice there is to choose carefully the songs you include in the demo. First, a club owner is like the record company exec..... they will rarely listen to more than a minute of the demo unless they have nothing better to do. Most are very busy and all you have is 60 seconds to convince them to hire you.
So, put your best stuff first. Choose something that you play really really well. Something that sounds full and exciting. (unless you are the holiday inn lounge lizard review cover band)
What we did was record a verse and a chorus and then into another tune..... basically a medley of the better tunes we did. The whole tape (yeah it was in the days of cassette tapes) was about 8 minutes long and I doubt any of the club managers ever listened to the whole thing. By the way, nothing on the demo tape was an instrumental. The only instrumental we did play "by request only" was WIPEOUT and I don't think we put Wipeout on any of the demo's. We had a really nice (and costly) booklet style promo package with pictures, gear, reference club list, and song list for the managers to see who we were and what we did.
Many managers did not care how good the band was as long as you didn't run the paying clientele out the door and you managed to keep the people dancing, happy, and drinking. Most booked us on reputation and word from other bands they currently used.
Anyway..... that's my 2 cents worth of booking advice. And yeah, we were full time, very often playing midweek and week long gigs as well as some nice weekend events and clubs. I was the booking agent for the band.