Put a quick connecting fitting on your babystay and remove it for the downwind legs, re attach for the beats if it's deemed necessary.
Leave the engine unless it doesn't run.... if you have the forward engine model you will really disturb the trim by taking it out and hanging an outboard on the transom. Also the Y30 is a fairly tall boat, so using an outboard effectively is going to require some fairly involved brackets/mounts. You'll likely spend more on the motor and mods than you would on a good folding prop (there's always mail order/on-line shopping)
Aside from that hanging outboards on boats that didn't originally have them is just plain ugly.(JMO, of course)