Mulch--How Deep? and Oak leaves and evergreen needles

Yes, I always say 18 to 24 inches deep, at installation.  The first year, this will be your growing medium, while the cardboard or newspaper is smothering the weeds below. 

After winter or a few weeks of watering the 18 to 24 inches will settle to less than HALF of the original height.

The goal, before planting, is 8 to 12 inches of moist, settled mulch materials, above the soil surface.

If you have 16 inches, fluffying it does not count.   When I use old hay, I do not fluff up the hay.  It will settle more.  The beginning height is not the point--it is the end height that is the goal.  Fluffed materials  will just settle in on itself as it gets wet.

I don't bother to chop leaves, unless you are picking them up with something that chops them.  We are not mulching the soil with leaves and then planting into the soil.  We are creating a mulch bed, that we will plant into.  Leaves that are matted together are just a place for roots to grow between.  This does not cause an air exchange problem for the lasagna/deep mulch garden.

Oak leaves are fine to use, up to about 25%.  If I you have evergreen needles, I suggest us using them as the very top layer.  They look nice, and are slow to break down.  They will be good as the top layer through next year's growing season.  Then next fall they will be on the bottom of the 12 to 18 inches of materials you add next fall.