[MAS]

I don't know the answer to all of your questions, but...

The sticking clutch pedal is usually (read: almost always) symptomatic of a bad clutch master cylinder. They are not expensive to replace. Often the slave needs doing at the same time. So it's usually best to get them both done ASAP.

Also, regarding your dificulty in changing gears (at times)... this could be due to your clutch not being properly activated because of your clutch master and/or low clutch fluid.

The "drone" at highway speeds could be due to the tires. Maybe they need to be rotated? "Feathering" of a front tire can make this sound.

The stock stereos are not worth repairing. I suggest a complete replacement: with a CD player and new speakers, front and back. Almost any reasonably priced 4x6 speakers will be an improvement over the stock
Blaupunkt 4X6's. You can get good 2 way 4X6's for under $120/pair, and a reasonable high power CD player for about $200. If you get them installed at a pro shop, you'll probably be looking at under $600 for a more than reasonable sounding system.

-MAS