MySQL: columns with mixed character encodings, and finding columns which have multibyte data
The data size is not 4x.  English text, even in utf8mb4, takes only one byte per character.  Trademark(etc) symbols are multi-byte.  Then ones you mentioned are only 2 bytes.  Emoji and some Chinese is where 4 bytes become necessary.

Don't create indexes on large columns.  Don't create indexes until you have the queries -- derive the optimal indexes from the queries.

It is perfectly fine (in MySQL, at least) to have one column be latin1 and another be utf8mb4 (etc).  And both of those can be in the same index.

I suggest making a couple of passes over the data.  First bring everything in with utf8mb4, no indexes, wide columns (eg TEXT).  Then analyze what you got -- SELECT MAX(CHAR_LENGTH(col2)), ...; test for non-latin1, etc.  For the second pass, re-do the schema to be closer to max len, etc.