Hadn’t paid that much attention to the weapons on the tanks - I’d assume they were an abstraction - but super easy to change.
We have found armoured cars are astonishingly good, stabilised HMG, mobility, armour. Overall it feels the vehicle rules are a bit weak. We are playing in 10mm so plenty of vehicles is no challenge.
Summoning - there isn’t a hard rule to stop you summoning more than 1 of a creature. But there is a practical limit in that summoning dice are hard to accumulate so its hard to get more than one in play at once, and summoned creatures tend to be priority targets so don’t last that long.
I think there is an implicit movement of the grounds inline with the receding seas - it lets you put some cool bone models on the table.