If your seed trays are A4 size, then you'll need 16 trays to make just one square metre of meadow.
Personally I'd sow just the flower seeds (no grass), in invididual cells in a seed tray, and raise them as individual plants (ideally you ought to have done that last Autumn).
For a simple life, forget about the grass altogether. Just below is a snap of a municipal wildflower meadow not far from me, taken last Summer. It's just solid wildflowers. No grass. I think it was planted up in the Spring, by council workmen. You won't do better than this..