Variable-length columns like VARCHAR or CLOB should not balloon the size of your Tag table just by adding them; assuming even a moderately sane dbms those large and sparse objects would be stored in separate data structure (thing 'string pool') so you pay for what you use.

BTW my earlier comment was meant to say "Episode (left arrow) EpTag (right arrow) Tag" but I used angle brackets and the middle bit got swallowed by HTML.