how much blob data can mysql handle?
That's less that a gigabyte?  MySQL can handle a terabyte or more.  MySQL could handle 10 blobs in each of 10 million rows.  Or more.  "Blob" is not the issue.

As for "performance issues", that's a question of what indexes you have, what queries you have, etc.  Please provide more details:  SHOW CREATE TABLE; some sample queries; what type of data is involved (eg images); etc.