MDF Panel kitchen doors

Hi I am making some kitchen doors to suit my existing kitchen. I have use a router and made the doors out of MDF for the stiles and rails and marine plywood for the panel in the centre. I will need to paint it white but I need to know what to use as a putty or filler in some of the joints and also if I will have to prime the MDF. Could anyone help me with these next steps in the process and tell me what products for a filler and a primer are the best choice

Terry