I want to think you can open the trunk without taking drastic measures. Be aware that the trunk lock can also act as a central locking system for the doors as well as the trunk, locking and unlocking depends upon turning and pressing in the latch in different directions. Experiment.
So far so good on the bulbs; removing the entire light assembly allows you to see if any corrosion has set in in areas not readily visible. This happened with my car, I found out about it as a fluke, but was able to catch it in time to avoid further problems.
Changing the fuel filter is a DIY job, no special tools required, but you do have to put the car up on jackstands or on a lift to get sufficient access and workspace, and you need to be prepared to catch some inevitable spilling of gas. By all means pick up a Bentley manual which shows how to do this and other tasks.