I don't have the hard experience of playing all these instruments, but I do have some bits that might help.

Overall that Yamaha will be your most diverse option. Classic rock is a mixture of single and double coil sounds, as well as semi/hollow bodies depending on what band you look at. The best way to cover all this ground is to either have split-able humbuckers (a feature that will put you in a higher price bracket), or have access to both single and double coils, which the Yamaha provides.

A co-worker has that GAX and he's a metal guy through and through. It should be noted dual humbuckers would cover later/hard rock as well as metal, but if you're also looking at earlier stuff from like the 60s you may want to keep that single coil option.

I wanna get a starter guitar? Figure I should start actually learning to play.

Does anyone here play the harp, by chance? Would it be completely unreasonable for me to buy a 19-string pixie harp (with no prior musical experience)? I initially wanted to buy a santoor/hammered dulcimer, but those are a bit over my budget. Would a lap harp or lyre be more realistic to start with?

So... I'm seriously considering learning guitar. I'm much more interested in acoustic than electric, so I'd buy one of those.

Three questions for you guitar aficionados (esp. Plankton and Chula):
1. Although I'm looking for a starter, I'd like to get something of fairly good quality. What brands should I look for?
2. How much should I budget?
3. What features should I look for? i.e. strings, neck, etc.

Strings and a neck would be quite beneficial.

Bloody literal Germans :D

Takamine is a good starter brand but make sure that you don't get a clunker.

What IS your budget? You need to start there. Have you ever played guitar before? How much will you be able to dedicate to it on average the first 3 months?

$300 is the most I'd want to spend. If I could get something quality for $200 or less, that would be great, but I'd rather spend a bit more to get something I'll enjoy playing.

When I was younger, I used to hack around on a guitar we used to have around the house, but I probably stretched the definition of "playing." I am decent on the ukulele, though.

I'd say 30-60 minutes per day would be a reasonable estimate. I should stipulate that I learned piano the "right" way, by playing lots of scales and arpeggios, and I'd take the same fundamental approach to any other instrument.

The thing is that I've reached the point where I'm realistically not going to get any better at piano without an inordinate amount of work, and I miss the fun of getting better at an instrument.

If I were to start all over again, I'd go with something like this:

Fender Classic Design Series CD-140SCE Cutaway Dreadnought Acoustic-Electric Guitar Black | Guitar Center

You'll have a great starter guitar that can also be plugged in so you can test future effects and amps, but make sure to get it set-up properly with any truss rod and saddle adjustments if necessary. Also, starting with an acoustic is, imo, the best way to develop muscle memory early on since fretting one takes a little more effort than most non-acoustics, but make sure you're learning proper technique and hand placement first:

https://www.guitarhabits.com/how-to-...-positioning/#

Like anything new, it'll feel awkward starting out but keep at it and you'll find a comfort level that will be the foundation of your musical journey. Start off proper and build that solid foundation, but most importantly... be bold and fearless in your discoveries. Good luck my young friend.