It sure sounds like you have a small bio load unless you have a ton of corals and inverts that your not mentioning or all your fish are 2feet in length
Skimmer buildup in the neck is perfectly normal and can have an impact on what your skimmer pulls out of the water. I empty my collection cup and clean the neck by spraying it with water, however if you scrub the neck clean you will need to go through the "break in period" until you at least get a film on the neck. Most reefers I know will NEVER scrub the neck 100% clean due to the above reason, not to mention fine scratches in the skimmer neck can impede it's performance drastically. Just spray off the heavy gunk and leave the film on the neck for better performance.