How difficult is it to carry out some of your own maintenance and which tasks could you do by yourself without having to invest too much money in tools/equipment?
That really depends upon the capabilities of the individual concerned. For someone possessing a reasonable level of mechanical ability and understanding, there is actually quite a bit of basic preventative and routine maintenance which can be performed on a privately operated aircraft by the registered owner/pilot of that aircraft.
Part 43 appendix A (c) contains a list of such items.
Naturally, knowing one's own limitations is more than just advisable and consultation with a certificated A&P mechanic is highly recommended before undertaking any work or making any required mx log entries. Obviously, possession of, and familiarity with the aircraft service manual and basic mechanic hand tools to be used is also necessary. Working under the advise and council of the A&P (IA) who will be handling your annual and/or other maintenance is a great way to increase your knowledge and awareness of your aircraft's mechanical condition and mx status at all times. Most owners I've known who participate in maintaining their aircraft tend to have very serviceable airplanes that yield fewer surprises over time. But it requires a long term commitment on the part of the aircraft owner to become proficient and knowledgeable enough to do much good.
This is not the kind of thing that people do if they are in the habit of taking their car to the dealer for an oil change or hiring people to do simple home maintenance tasks. But if you prefer to mow your own lawn, paint your own rooms or change your own oil, doing preventative maintenance on your own plane might be for you!
As to using a light single to make a short commute in lieu of driving, why not? Just remember the old axiom: "If you've time to spare, go by air!" That old saying comes from the first generation of air travel, but still has some applicability to modern private light plane operations. Things happen. Like weather (even in SoCal, winds, rain, fires, low ceiling and vis. They all happen) Even with IFR capable plane and pilot, there will be a fair number of days when driving is more reliable, no matter how frustrating and tiresome. In other words, unlike driving in SoCal, light plane flying is something you do because you prefer to, not because you have to. Never let something you set out to do for personal gratification turn into something you HAVE to do. It ruins it...
Best of success,
westhawk