Biggest problem with sidearm is that your breaking ball will not drop! Another major challenge is that you give left handers (or right handers if your lefthanded) a very very good look at the ball as it leaves your hand.
These are two major problems for side arm pitchers, and why most of them on the major league level are "specialists."
Coaches that have rosters will load up batters with you oposite side. They will get a good look at your pitches, and will not fear your breaking ball. (This is huge!).
When the batters see's you once a game it is usually OK, but for three go rounds you better be mighty special!
If you are a righthander you must develope a good sinking change-up (which should be farily easy).
Unless you are wanting to be a specialist, I would not drop below low 3/4's as a starter, Ian.