Mulches aid in suppressing unwanted plant growth, maintaining soil moisture levels, keeping soil temperatures moderate, and adding organic matter (if vegetative materials are used) to the soil. However, because they do help hold moisture mulches can be bad for wood structures just as being buried in soil would be.
Mulches should be in place during the hottest, driest parts of the year, like now, so if you will be using mulches now is the time to put them in place.

Thank you kimmsr- and I apologize for taking so long to say thank you!

In the end, I decided that I really need a lower-maintenance patio/garden area. So I'm covering some of the dirt with resin pavers and another area with rocks that I've been finding all over the place in the soil. I think they were used as mulch by previous owners.

Next year, I'll so some containers. But I really bit off more than I could chew this year.

It's OK to have mulch up next to a fence as long as it's not touching/covering the bottom of the boards. The rocks are a good solution.

If you have perennials, bulbs, etc., it's good to have mulch in winter as well, to moderate the soil temps and reduce freezing/thawing cycles. So don't hesitate to mulch late in the year too if you can.