intended as having many more will explode the ram

Is not one kind of Sources the upper limit only 500,it's all Sources
I was able to fill the Custom map 1.8 version with Sources,half of it cannot be achieved now

This limit is applied to the amount of different types of tiles, you can have any amount of the same source tile and it will still count as 1.
I'll add some kind of a hint to the inventory if there are too many tiles.

@therainycat For sources specifically, stack sizes count towards the cap instead of amounts of stacks
https://discord.com/channels/590288287864848387/590290050051342346/1292128389943263284