Decorating mdf cabinet door

[yartin]

Hi
I am decorating an mdf cabinet door, I did first sand down 60g old paint then used wood filler, sand 200g the applied two coats of Zinnser bulls eye 123 primer. I am not entirely happy with the state of the door as needs more fillings to do before a top satinwood finish.
Can I apply filler directly over the primer or does it need sanding? Shall I use again wood filler or can I use any filler?
TIA