I currently run a bubbler and I believe the one thing you don't want to skimp on is the airstone. More air better roots, better root system BIGGGGG plants. As for multiple plants on the same solution. I do have 3 in a 18gal storage box(cost $4 at dollar general). I run three air pumps in mine. Here's a link to pics of my current grow.
http://forum.grasscity.com/attachmen...001_edited.jpg
By the way, I think you will have an easier grow if you keep them seperated, I'm constantly having to adjust, one plant keeps wanting alittle more mag while the rest are happy without. So its a juggling act.