Bridsmaid dresses

As long as you consult with your bridesmaids on their budget, you're in the clear.

Different colors and materials are very common, and even celebrated now-a-days. I'd say let your bridesmaids pick out of your color choices and let it evolve naturally rather than dictate what they need to wear. It's more fun for everyone that way really (and less stress involved for you!)

I think this is very much up to you. As long as you're aware that even the exact same colour will photograph differently if it is in different fabrics. Ie, chiffon vs satin vs crepe or whatever.

do you have pictures of the dresses you're considering? I think this would make it much easier to see what you mean, and determine whether they will clash or not. I think generally speaking, a floral fabric is going to be more forgiving in matching with a plain fabrics than trying to match two plain fabrics might be. I also think trying to match several florals to each other would be quite hard, but might look lovely too - it just depends on what your vision is, and the vibe you're going for!