Subject Charset UTF8 or ISO8859_1 for new DB with CI + AI

I've used FB for years with ISO8859_1 charset and collation.

Now I designing a new DB for a big app update in FB3 and wonder about this charset and collation. My goal is to avoid having to UPPER everything for comparison searches.

For test purposes I am using UTF8 and UNICODE_AI_CI and I like that I can now don't have to worry about casing comparisons nor accents or other special characters.

In fact, all the stored data in will be in the regular english-us alphabet with maybe a little in spanish for things like "japapeƱo", but still all single byte chars.

Here are my questions:

1. Is only one byte used for storage for english and spanish?

2. Is there any CI + AI collation for ISO8859_1?

3. Is there any downside to using UTF8 and UNICODE_AI_CI over ISO8859_1 and collation ISO8859_1?