Possibly the best thing you can do if you feel the urge to make significant or complex repairs on your guitar would be to get one (or several) of the decent books on "how to build your own XXXX guitar." (Different books deal with different kinds of guitars, so try to pick one that's for the kind(s) you have.)

Study really hard.

Even if you never build one, you need to know a little bit about the innards of the beasts, before you poke hard enough to break the skin and make your pet mad at you. IF you don't treat them with respect, THEY CAN AND WILL BITE YOU, although some real repair shops (like appliance repair persons) do get a giggle or two out of bailing the "home fixers" out of the problems they thought they were solving.

Building one pretty much "from scratch" isn't really all that complicated, once you understand what you're trying to do and the conventional ways it's done. This usually comes together at about your own third of fourth actual creation(?). The hardest part for most may be getting a decent finish on what you create (which may not actually be a guitar in any conventional sense, but is pretty likely to make more or less pleasant sounds, and should make you proud.)

If you study hard enough at the beginning, you'll probably figure out that the parts and materials for a DIY build are going to cost you about as much as buying something better than what you're likely to build, after someone who practices more has done the hard stuff for you; but by then you'll know enough to have a good idea of what repairs you can do safely and what you should take to someone who "knows the real secrets."

John