What are the highest skill level sets on tiny tower

The great things about bitizens is that they never seem to need to sleep. Thankfully you don't have to manage your bitizens personal concerns in this game, as the focus is the tower. Your bitizens will work 24/7 without any loss of productivity, so long as you can keep your shops stocked. So, yes, shops should be open at all times.

If you see them complaining in the Bitbook, I think that's just the developers way of adding some personality into the game. :) The only way to make a bitizen happy in the game is to employ them in their dream job. Failing that, until their dream job opens in your tower, best practice is to match them with the area that they are highest in according to their profile. They will at least remain content until such time as their dream job opens and you reassign them. So long as you can match them with a job of interest level 5 or greater, they will be content. Anything less than 5 and they will be unhappy in their job.

You will see a severe decrease in demand for all non-food businesses (which applies to ALL businesses of that type, not just the extra ones) when you fail to keep businesses even. The demand % you see directly relates to the amount of people that will visit each floor of the type. At 100% demand, each floor gets 10 bitizens (purchases) per minute, each 10% demand drops, you lose another bitzen/sale per minute. The drop in sales will be substantial.

From the Wiki:

demand = total commercial floors / ( 5 × total category floors )
A floor of a lower demand category will draw less customer traffic than one of a higher category. For this reason, it is beneficial for the player to keep demand on all floor types high by building from each category evenly. The following table illustrates the approximate impact of various demand levels.

Thanks to demand, it's better to have food floors you just don't stock than to not have them at all, so just buy some food floors, you don't even have to stock/employ them. You can spend a tower Buck per floor to shove all your food floors together and ignore them as a set if you wish.

If you don't put employees in your food floors, you can save some bitizens for your other floors, thus needing less residential floors per commercial floor. Residential floors don't affect demand.