wildflower meadow

Hi all,

Am going to try and sow a wildflower meadow at the back of the garden this spring. Just thought I'd run it past all you experts on here. The area was grass but I would say very poor in nutrients. I stripped off the turf and have just dumped a load of old sand/subsoil from beneath an old patio on top of the ground. Am thinking this will create quite a good base as it will be very nutrient poor.

Is there anything else I should do other than to sow the seeds in a few weeks time? Was thinking of getting mixed wildflower seeds as I'm not sure what is going to do well. The soil is quite heavy clay below so probably not ideal for poppies, cornflowers etc. Any species I should particularly go for?

many thanks!