Does column size increase break SELECT *?
"Maximum row size for mysql" is the terminology you are probably looking to search for - that finds a useful stack overflow page at https://stackoverflow.com/questions/10349361/mysql-how-to-workaround-the-row-size-limit-of-66-kbytes

That suggests a maximum row size (excluding blob types which are stored off-page) of 64Kb, and has a couple of useful looking links with more detail.