That's a good analysis, and the harp and electronic keyboard are both easy instruments to learn. I would add that the guitar also allows for:

• nearly mindless strumming that will still produce many interesting variations on popular chords

To get, e..g, different kinds of E Major sounds on a piano, you have to remember the finger shape for E Major and move it the correct number of spaces up and down the keys. To get that on a guitar, you just move one hand rapidly back and forth, hitting different strings at random. Maybe you occasionally release a finger on your nondominant hand.

Out of the instruments that are usable for both melody/soloing and harmony/accompaniment, the guitar family has the clinching virtues of being cheap and portable. Like keyboard instruments it is also applicable to virtually any genre of music. K/b instruments are more suited to complex material (hence their use in composition), whereas the guitar family allows more expression than instruments that are essentially controlled by switches.

These advantages entail one overriding disadvantage: ever other bugger plays one. So it is proportionally harder to get into a band or college. If you want gigs,play something cumbersome, like drums, double bass or euphonium.

• Rock, pop and folk music, the things guitars are popularly used for, are quite simple, so you don't need to be able to play well at all to get music out of the thing. (Think how many punk rock bands could literally hardly play when they started. "Here's one chord, here's two more, now form your own band.") Also, you can get a guitar and amp that are good enough for your whole career way cheaper than the typical good classical instrument.