My question is, how often and how much maintenance should I be doing on my bike? What is regular and can I wait on some things?
You can always wait. But I think you're asking what can be done to prevent mechanical failures on the trail.
It's hard to make a blanket statement that is meaningful. For instance, the drive train will usually start to shift poorly before it fails if the problem is dirt. But a worn out chain will take a cassette with it and may show no symptoms until both are shot. Measuring the pin-to-pin distance on the chain is good preventative maintenance. 12 1/8" is too long for 12 links. Two seasons on a chain is about it if you ride much.http://www.kronowit.com/bicycling/chainstretch.html
I usually don't get my shocks serviced until they leak or make noise. Most manufacturers recommend dirt seal cleaning or replacement on a yearly basis.
Derailleur cables and housings don't last forever. They tend to pick up grit in a mud ride and should be inspected afterward.
Wheels are a tough one. Disk brakes make it possible to ride wobbly rims and still get good braking performance. In my experience, wheels don't tend to last once the spoke tension becomes uneven. Tim's method is definitely better than nothing, but a pro mechanic is worth the money for truing wheels in my opinion. As William pointed out, Yellow Jersey takes pride in their wheel building reputation.
Always run more pressure in your tires at Blue Mound than you would use elsewhere. It's a bad place for skinny tires. It will destroy ordinary tires run as a Stan's conversion. Blue Mound will make you a better rider, but you will pay.