What volume developer is best to use with this? I have the satin cover grey silicone enhanced developer and I think it is only a 10 volume.

I use Satin 7N color with 20% developer and Grey Magic drops. Works great for me and has for years.

Can I use any developer ? I have 20 volume wella developer?

I use developer, 2 parts to one part color.

What color do I get need platuim blond?

The higher number, lighter color

Can I use the 10vol developer to take my bleached hair back to a light ash brown?

You must always FILL blonde hair before you go back to brown, with a red filler. Red filler puts the pigment back into the hair that was lost in the bleaching process. Then the brown color applied will likely be accurate. If you do not fill the hair, it will likely turn green and dull. Always look at the underlying pigment chart if you plan to go in reverse again. Best of luck, I know it's 8 months later, sorry.