general questions from a novice

Hello all,
Here are some very basic questions:
When growing bulbocodiums, what type of soil or top-cover is best? From the many pictures I’ve seen, it looks like coarse rock or gravel or coarse sand is at least covering the soil.
Also, when growing crocuses and snowdrops, can I expect them to naturalize, multiply or divide in the same way that daffodils do? Or, should I be planting them in clumps from the outstart?
Thanks, Niels Benatar