Depends on how big the mealies are, really. You could feed twice as many small ones as big ones and it'd be about the same amount. And it partly depends on your hedgie, if you have a runner like Lizardgirl does, you could feed mealies probably every day and he/she wouldn't put on weight. If your hedgehog isn't a big runner though, or is prone to putting on weight easily, you wouldn't want to give mealies all the time.
For Lily, I've been feeding her a couple of mealies every day, actually, sometimes big ones, sometimes small ones, and I weigh her every few days. Her weight hasn't fluctuated much, so she seems to be fine with that, until I stop messing with her cat food and can start changing it up with other treats.
As far as I know, crickets aren't as fatty as mealworms, but I've never fed them to Lily, so I don't know how many of those to feed. They're still considered a treat like mealworms, though.