The full rules for crowds can be found in the rules on p. 15 and p. 28: LINK 1.42 beta
The entire board in Guilders have Loot. All buildings, civillians and crowds have a Loot I token - this is petty cash mostly. If a thief steals a Loot I, they will be able to cover their upkeep and perhaps put a small item or few coins in the guild treasury.
Buildings with Loot I need to be lockpicked (a skill availble at start for thieves) or smashed (will cause alarm and bring guards).
Then there's Loot II and Loot III which will bring in a lot of extra cash and items for the guild.
Crowds are a 3" round base with miniatures (I use three on mine). The standard scenarios have 4 crowds (two placed by each player) and some single civilians. A crowd has a single Loot I token.
Crowds can be pickpockted or knocked down (one is stealthy the other will cause alarm and bring in the guards).
Crowds (and single civilians) move randomly at the end of each turn. In Reality's Edge (cyberpunk game) the crowds moved very little and often got into a 'bump' situation. Hit terrain, move rest of movement the other way.
In Guilders crowds move d10" in a random direction. They don't bump into stuff, but move around it continuing in the direction rolled. So they won't end up static.
Guilders can move into crowds (hide from guards), covered from shooting and will then move with the crowd when they move. So it's a good way for a thief to stay on target (free moving) more actions for trying to pick their pockets.
It really is quite fast moving all the civilians. Roll d10, use the top as direction, move crowd.
A concept in the game is Overall Alertness. The more Alarm the guidlers cause, the tougher and more guards will enter the board. When Overall Alertness gets to 15 (the guards are hostile at this point) the crowds and civilians will stop moving randomly. They will then move directly towards the nearest board edge instead (running for their lives, as there is obviously a lot going on in this part of town). Guilders can still be inside a crowd base - it's a good way to escape the board.
Number of civilians
So in a standard game of Guilders, you will need 4 crowd bases (12 models if putting 3 on each) and 4 single civilians - so a total of 16 civillian models. Nothing stopping you from making a crowd with a herd of sheep, a crowd being a small wagon etc. Important part is that it's a 3" round base really.
I'll drop a post about making crowd bases later. Made with cardboard and xps foam. But here's a quick shot of one before painting. Made with small holes for the civilians, so they wont fall off.