What are you good at craft wise? What are you interested in learning to do? Can't make suggestions till those questions are answered.
Right. Start with what you have. If you have some experience with wood or electronics, think along that line. Enumerate your tools, try to avoid buying a lot of new ones (you won't, but try). I have built lots of scale models about 10-15 years ago, I'm glad I still have the tools. I think a lamp is one of the best things to start with, as they are actually useful. I'd have a hard time explaining the necessity of goggles (which I don't want to build anyway). A nice lamp is self-explaining. Also a good gift. I have nearly completed my first one.
Gears, machine parts as ornaments should be used sparingly. True applications never have surplus cogwheels or sprockets glued onto them as decorations. Rich and detailed ornamentation is fine. Victorian and even modern vehicles were often painted or decorated with motifs, either nonfigurative or traditional: wings, natural patterns, symbols of power. But these are what they are: liberally swirling ornaments, not trying to mimic function.
When you can display anything freely, without the urge to make it _logical_, that's called painting or sculpture. In fantastic literature, fantasy - as opposed to science fiction, where you cannot just conjure up anything by magic, but have to find that monster a place in the _system_.
Of course you can make an installation or a picture by attaching mechanical parts to a canvas. Some parts definitely look good by themselves, the inherent beauty of metal and machinery can make it a nice eye candy. Same goes to jewellery. But a working piece of equipment should look as if it was meant to be produced and used functionally. Car design is a good source for this principle. While many cars expose some of the engine parts to look good, there are no muscle cars with a piece of piping or a glued-on manifold that has absolutely no use.
Moreover, it is much easier to show off your work when it actually works. To laymen, your painting may look like some demonstrational material stolen from a factory. Some may ask themselves: why did this guy put a cogwheel on his wall? But if it is, say, a lamp, then even if it appears weird, its still a lamp, its there to illuminate the room, and within that group of useful items, it is definitely eye-catching, even if made of basic plumbing parts.
