Spacing can vary according to the effect you want to achieve. If you are planning to move the bulbs after they bloom, you can plant them as closely as you want. Otherwise, see the recommendations below. Planting depth is the depth to the top of the bulb once planted, not the depth of the hole.
Depth can vary, too.
If you are planting late or want the bulbs to bloom a bit later, you can plant them an inch or two deeper. If you want to extend the bloom season on a mass planting of one variety of bulb, you can plant some an inch higher, some an inch deeper and some just right. That will give you an extra week or 10 days of bloom season, all with the same variety bulb. Daffodils need a few more weeks to get fully rooted out before the ground freezes, so they should be planted in late September thru mid-October. Fall blooming crocus and Madonna lilies should be planted as early as they are available.