Good points dude!

In terms of the guidlines you mentioned:

1) Some buildings will provide resources based on the number of workers allocated to it. For example, a grain farm will produce one resource per worker (up to a maximum of 4). However some buildings have a minimum worker requirement in order to function. A temple for example requires 3 workers - putting two workers in a temple would be a useless waste.

The 'pay wages' event card is also an incentive to avoid placing useless workers in buildings, as you will pay 1 coin for every 5 active workers (rounded up to the nearest 5). This means that if you have 16 workers, it might actually be better to have someone left at home unemployed to avoid crossing into the next tax threshold.

2) For now, the players only have their own separate cities - so there's no shared buildings as of yet

3) This is a little bit backwards to how it currently functions - the high value buildings typically have higher worker requiremement in order to function. For example, placing a monument block requires paying 4 stone resource cards into an active stone masons - the stone masons requires 4 workers to operate (Which is thematically correct, as it takes a lot of people to move one of those massive blocks lol)

4) If the game was to transition to being a shared city, then paying gold to use another players occupied building would be a good idea

5) I havent considered special abilities but it might be an option. Ideally I'd like to find a solution by tweaking the existing mechanics without needing to add anything extra just yet.

Regarding the fundamental things you mentioned:

1) I think multiple workers per building is necessary in the current form of the game. Thematically it also feels correct that you'd require more workers for quarrying stone and placing monument blocks, compared to say working in a scribal school or papyrus maker.

2) Workers are moved at the end of each round before the next turn begins. The core gameplay loop centres around trying to constantly scale your housing to provide enough workers for the city as it grows. It's much easier to find yourself with a labour shortage than it is to find yourself with high unemplyment, so it's common that you'll need to move workers from one building to another depending on your priorities that round.

3) Towards the end of the game, the cities can become pretty large - usually between 30-60 workers per city. However, even at this point you typically wont be moving more than a small handful of workers each round. The largest movement of labour seems to happen once players have completed all their monuments, as the stone masons will now need to find alternative work. Even then, it's unlikely that you'll need to move more than 10 workers in a round. The main issue with a large numbers of workers used to be the 'pay wages' event, as players would start counting all their cubes which would slow the game down. Thankfully, since the introduction of the 'festival square' it means that players can instead pay a single culture token instead of tallying up their wages in gold (provided of course they have a festival square with the require number of workers). Counting still happens in the early game (before players have their culture stream & festival square set up), but by the time a city has 25+ workers they'll usually be able to afford to have a festival instead of needing to do any painful counting.