Hmm, it really depends on how much time you spend enjoying each hobby, I don't normally spend much time in each hobby (even if I wish I could), for example... Even though I enjoy working on firearms, I live in a suburban area... Which means I have to find a place to shoot the firearms, which I did. There is a range about 25 miles away from me which I am a member of. Since I live so far away, I go to the range often enough, but still not very often. This means that I can take my sweet time working on multiple projects, which means I'm not always working on firearms (If I could I would though ^-^)
Same with the cars, basic upkeep isn't as hard as it would seem so it doesn't have to happen often.
That's why I have all of the free time XD.
So the number of hobbies doesn't matter, and quite frankly the fewer is sometimes the better. I'd rather be really good at a few things than average at a lot of things.