Go for it. There are lots of stories floating around that if you are trained primary you can teach secondary but not the other way round, and some say if you are trained secondary you can go into primary but not the other way round. Who knows what is true, but I know many who have made a switch no problems. Welsh speaking helps for primary since you need to be doing daily incidental Welsh now. Being male can help, well, so rumour has it. I made the switch over from secondary to primary and love it.