Next step- redesigning commerce limit, making it nation instead province based, and taking advantage of excel formulas to auto calculate stuff.
So here it is. Notice that this is a) subject to balance changes b) won't be introduced immediately, but rater 2 turns from now, giving players option to fix things before they happen, so if your limit is low, you still have time to fix it all.
Formula is a bit complicated but actually I'm not calculating it, but excel.
City provides 20 commerce limit, farms 15, fisheries 10, windmills, herbalists (aqueducts, infirmaries if someone gets creative)... all increase it.
Usage of that capacity is:
Your domestic income + half of your domestic income + twice what you pay for unit upkeep and all that divided by your stability %. So at 50% stability you use twice as much commerce, and at 200% half as much.
Have in mind that commerce limit may vary by turn as well, so steer clear of it if you can, so that bad harvest won't cause famine. If can fluctuate by up to 10%.
Opinions?
Will tweak agriculture to increase this limit. Kuriotates have increased commerce limit due to their project of Urban Developement.