Are there any "rules" regarding this? So for instance, if my demo is only 50-100k, what's a good daily spend limit I should place on this campaign, or does everyone just jack up the daily spend as much as possible regardless of the demo size?
I usually set a budget of no less than $500 if the demo is around 100k. Sometimes I even do $1k but that's when I am testing
How long does a campaign like that last if the demo is small but your spend limit is high? Is there any reason I should limit my daily spend at all?
If it's less than 100k demo try setting it to spend 100/day/camp. Meaning, you roll out 1 campaign at 100/day, if you want, roll out another at 100/day. Then optimize it according to the volume/roi/CTR you get by pausing the campaigns rather than fiddling with the budget set on 1 campaign. I find sometimes fiddling with an already high CTR campaign will screw it over.