I suggest that you remove the mulch, or at least some of it, maybe down to about 2 inches just to reduce any weeds. Yes, you can side dress with fertilizer now. A good choice comes from Dixondale Farms.

And I say to leave the mulch! If it makes you nervous, just divide the mulch where the plants are. As mentioned on another thread, we put that much straw on a 10,000 clove field and there ain't anybody going to remove a single straw! Straw mulch is very porous so it won't form a solid mat like leaves will.

Martin