Layering is an old & very effective practice.

Just be sure you also "stagger" them so that each one has a straight shot to the sunshine;
if you put the bulbs exactly on top of each other, the deeper ones have to take a detour around the shallower ones.

don't know what to tell you about spacing them around your perennials;
maybe you can get answers from a garden club in your area?

Agree that layering is fine and a nice way to get a sequence of happy blooms in the spring.

For spacing, you'll want to give your perennials and shrubs plenty of room to breathe. When I first planted bulbs I tucked them underneath other plants, but soon it became clear that was a bad idea, as the shrubs grew right over the bulbs. So I'd put the bulbs out at the perimeter of the other plants. (The size of the perimeter depends on the size of the plant.)

Thank you both!

For planting around perennials, it depends in part on their respective schedules. I actually planted crocus in the same hole as my peony roots to mark the spot where their tender little buds would appear. I also have early and mid season daffodils planted very close to peonies. I love allium with white peonies - the foliage on allium is so ugly that I'm thrilled for the peonies to hide it. I also plant early stuff around hostas.

First time planting bulbs, huh? Have fun - they're very addictive! :)