For handguns, generally no, if you're using carbide sizing dies. Bottlenecked rifle cases will need to be measured, trimmed/chamfered if necessary, and lubricated for sizing. Crimped military primer pockets will also need to be reamed/swaged after depriming. Primer pockets may need to be cleaned/uniformed and depending on how anal you are, you may want to uniform flash holes.
FYI I use both walnut and corn cob media, and nu-finish. Both have worked well. Walnut seems to take less time on grungy cases, but as has been noted, corncob polishes better (takes longer though).
I've mixed them also with good results. Just make sure you don't overload the tumbler with brass so it can't move around. start the tumbler with media in it, then add brass handfuls at a time until you see the movement start to slow down. don't add any more than that IMO.
