My honest advice? "Double-dig" the entire area you are considering planting succulents in. You'll probably need to mix in some organic compost (composted bark, composted wood, humus, but NOT peat!) unless there is a *lot* of plant debris/natural compost in the area. Adding the organic material will broaden the range of species you can grow and will make fertilizer unnecessary. It'll be a ton of work, but in the end, you will have a truly awesome, well-draining, bed that will require very little maintenance.

On the other hand, succulents just *love* abuse. As long as the soil drains well, a succulent will grow in it, albeit possibly more slowly. In fact, lots of people grow really touchy plants in pure pumice... If you can pour a gallon of water into a half-gallon sized hole in your current soil without filling it up, you could probably do nothing at all, and get good results with most plants (especially native cacti and agaves).

If this is a major landscape project ($$$) and not just a small bed or two, I'd highly recommend finding a nursery that specializes in xeriscaping. Nothing, NOTHING beats the advice of an honest, professional gardener...

Show us pictures when you're done!!!