Check out this post and see if it helps:
https://forum.vassalengine.org/t/totaling-the-number-of-pieces-on-a-map/8708/1
The ‘ends movement’ map level gkc is the map/player hand’s last listed property… then you need a way to limit that to only occurring with a first move to the board (you don’t want it to keep adding 3 to your global with every shift of the card in the player hand), as well as potentially divvying up your global properties for each player (unless you want them all tallying together). So that post kind of covers that, or will hopefully give you some ideas. You wouldn’t need to combine them all as I did, but could have separate end movement keys tied to each board/player to help with keeping the counts separate. The earlier posts in thread may help too.
Anyway, any problems or questions, just ask.