There are several books out there about growing succulents in containers together. (Check for ones by Debra Baldwin.) I find that you can group succulents into the same planter quite successfully. However, there are some (Lithops, Fenestraria, many Haworthias, and P. neli for example) that don't want to grow well without special care and attention. And, if you are collecting really cool, rare, and/or expensive succulents treat them to a pot of their own.
If you want a mixed pot, here are my rules for growing succulents together:
1. Try to use plants with similar water requirements,
2. Never spend more than $2 for any single plant going in the pot.
3. Be prepared to experiment, as you are most likely going to kill some or all of the plants until you find the right combination for your particular area.
4. DON'T add cactus to the mix.
Here are samples of successes and not so successes.
It’s not the fall that kills you; it’s the sudden stop at the end.
Douglas Adams (1952 - 2001)