[Jeph]

1. Is it OK to drive the car? I have a 30-mile commute to work. I expect the CEL to return, but it will be difficult to bring the car to a technician for the next few weeks due to job demands.
Should be ok. Mine did the same thing. 2000 non-S. The CEL would come on intermittently. Maybe once every few days.

2. I replaced the MAF sensor last year. Should I bite the bullet and replace all four O2 sensors or just replace them as they go?
Depends on how inconvenient it is for you to make trips to the shop. I had just one of mine replaced and no problems with the others.

3. Is this an easy DIY job or should I leave it to a technician?
What's your skill level? Just don't take it to the dealership! It's not too expensive of a fix to have a specialist do it, so I prefer to leave it to some one that doesn't have a learning curve to worry about.

Hope this helps.