E0, as PBrain notes, unavailable in California. Mostly, that's because the federal EPA won't allow it to be sold in nonattainment areas, and it's easier for suppliers to just treat the whole state as if it were a nonattainment area. The state's fuel standards are mostly oxygenate-agnostic.

"Gasohol" has been around for a long time. Pretty much any car built since the early 1980s, or even 1970s if it was first sold in the Midwest, can handle the stuff, in percentages up to about 10% ethanol at least. 10% ethanol isn't going to harm anybody's fuel system for non-antique vehicles. Yes, if you want to get into high ethanol percentages, a more robust fuel system is needed - those vehicles are generally labeled "flex-fuel." And newer cars have fuel systems that can accept at least 15-20% - US EPA has proposed (and may have finalized) rules to bump the required percentage to 15% ethanol, which is in fact marginal for older (pre-1990) cars.

Originally, the oxygenate requirement was to reduce CO emissions from carbureted engines in the wintertime, when most violations of the standards occurred. It also reduces startup CO emissions slightly, though with modern feedback EFI engines that have quick-lightoff catalysts in the exhaust manifold (i.e. pretty much anything sold in California since around 2000) that effect is minimal. The requirement evolved, of course, to be a subsidy program for corn-based ethanol producers.

Because of the near-universal ethanol content, gasoline has a fairly short shelf life. Over the course of several months in storage, the ethanol will start to separate from the gasoline, and will absorb water. Obviously, this can produce operating problems. There are additives to reduce separation and extend the storage life of gasoline, but it's still best to use it quickly. Long-term storage of a vehicle with modern gasoline in the tank is not a good idea.

As for crud in the tank, yes, diesels are well-known for it especially in the older days. Low-quality, high-sulfur off-road diesel that stayed in storage for a long time was infamous. Most on-road #2 wasn't too bad, at least in the 1980s when I had a diesel, and these days it's all ultra-low-sulfur (even off-road and some marine) and often has additives to control the bugs. Still helps to know how to clean/change and re-prime a fuel filter, though.