It is up to you. That is the beauty of garden 'design'. Please yourself, not others.
My own preference is to keep single colours, even single cultivars, together but I am sure you will find others who just bung them all in together.
Again, I would plant Tulips and Crocus in clumps with about 3in. between them, depending on the size of bulb. Try it and see, you can always change them next year.

Like Vincent said its your choice? I plant in groups of type and colour, but over the years it tends to get a bit mixed as I forget exactly what is where when planting more. But I still like them when they come up. A group of say Tulipa 'Queen of the Night' can look stunning as can a group of Tulip 'Tarda' rather than single stems which get lost. Crocus look great when planted in groups of white purple or yellow. Why not look at some Pics of bulbs on Goypeadia that might inspire you?