Hi,
The Alto seem to have a good reputation on the forum, i've never used them personally but the general feedback seems to be positive from several people. You can get hardware kits to convert general cabs to be flown, however make sure that it is done correctly and securely - the last thing you want is for your speakers to become part of your dancefloor

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Flying full range or mid and top speakers is good advice and will make a big difference but bass bins or subs need to remain at floor level. Some venues build the cabs in to the wall space, others just keep them around the dancefloor but what you choose to do with these obviously depends on the venue layout.
Keeping the main volume on the dancefloor is again the correct thing to do, however if you find that the seating area is too quiet, or the sound echos then a good idea is to build around the seating area some good quality background music speakers - the JBL Control range are very good for this sort of application. Pipe them from a seperate low wattaged amp and you'll be able to keep your seated audience in touch with the disco but at a suitable level to allow them to talk.
You may find that you don't need to install smaller speakers because of the overspill from the dancefloor is adequate but it's just an idea which works well if the dancefloor is some distance away from the seating area, or the sound is muffled because the main speakers are pointing away from them.