Sorry to be answering your question with more questions.
You don't state where you are, or your soil conditions, or the mulch you hope to use.
Mulch is a very vague term. One can mulch with sand, soil, compost, leaves, straw, even rocks. It is a really long list.
Mulch can work both ways, keep things warm in the winter and cool in the summer. Stepping on plants is rarely a good idea, so before they emerge is best.
