I you're having a surface scum issue AND a big time hair algae issue, then it seems like it all points to water quality. Gotta get those excessive nutrients down, or cut down on lighting, or both. The other thought is that if your surface scum layer is really really bad, you're effectively shifting the spectrum of the light going into your tank - kind of like if your lights were old. That, I suppose, could snowball and cause other algae issues within your tank itself.
Regarding another idea about the surface skimming, check out my other thread in the DIY section...
I was having a surface scum issue also, and this has totally taken care of the problem. You might be able to adapt it to your specific skimmer or filter setup?
Regarding the clownfish and the little white bugs... yes, they do eat them - at least mine does. He'll swim along, stop, orient himself completely vertical just above the sand or rock, then pluck them right off.
Oh... and those baby snails don't need extra shells. They build/grow their own. If they're truly snails you're seeing, they do have a shell already. Perhaps they're not snails?