On the SLICE issue, I think it boils down to this; If business is doing so well selling whole pies and the workload is maxed out, then there's no need to sell slices due to the overwhelming demand of whole pies. That's the optimum scenario, but a wise businessman would also be prepared for less than optimum conditions.
If the whole pies are not selling at a fast and highly demanding pace, then it would be wise to put up a separate sign advertising SLICES. Slices sold at a higher cost per pie would enable you to trash any cold or soggy slices that were not sold in a timely fashion and you'd still break even compared to selling whole pies.
If I had any slices that were not selling and about to go cold or soggy, I'd yell out to passers by offering special deals of $1 per slice or even give away a those slices as a marketing strategy to expose more people to this NEW style of pizza that I know they will love and tell other people about.
So, from a BUSINESS perspective, SLICES equate to more work, more complication, but they have great marketing potential for expanding sales.
From a CONSUMER's perspective, SLICES equate to lower cost, better choice, more convenience, and an attractive offer to try something new.
Bottom line, setup your signs and have a game plan to quickly switch between selling slices and not selling slices as the demand requires.