In your new bed, don't dig more than about 15-20 cm. You don't want to go really deep and mix the underlying heavy clay with what little topsoil you have. Add about an inch of the manure, and an inch of your planting mix, dig again to mix it all well, and plant. If you ever do dig a bed really deep for some reason, try to keep the soils from various depths separate, so that they can go back in roughly the same order. Generally you can easily see the changes in color and texture as you dig.
Did you have other plants intended for this new area, or just the seedlings? If it's just seedlings, after watering them in, they won't require mulch until they get a little larger. You don't want to smother them. If you're transplanting larger fans, then plant, water in, and mulch as normal.
