Always cover the tops of the ceiling joists to make sure the insulation is deep enough to reach your target r value and to prevent thermal bridging the heat loss that occurs through the wood framing.
Attic walkway over insulation.
Place a 2 inch by 3 inch board directly on top of the joist nearest to the edge of the attic with its largest.
If you can make the walkway 2 wide it most likely would not be necessary.
The blown in insulation can be blown right over the ductwork.
However if you need to make it narrower i would recommend standing some unfaced blanket insulation on end along the edges of the walkway to hold the loose.
If you displace insulation in order to move around in the attic don t forget to put it back as you leave.
I would recommend fiberglass blown in insulation rather than cellulose because it is not conducive to insects.
Work from the perimeter of the attic toward the door or hatch so that you don t trample all over the insulation you just put in.
The trail you leave in the attic can easily end up tracing a path on the ceiling below.