You could hunt turkey with this setup as well.
As far as deer hunting using slugs, you'll definitely want to test different slugs to see what groups best and the distance you can accurately hit about a 6" circle consistently.
Since you got the shotgun at such a good deal, if it were me, I'd look for a dedicated slug bbl. and a multi-choke bbl. They can be easily found very reasonable and you may even be able to work your 30" fixed full bbl. in on a trade.