Wouldn't a low density MDF have to be called LDF?
It looks like your setup is for high vacuum, low volume. That is the method I currently use on my mill, and it works fine until you open a single hole to the vacuum chamber. With your small fittings, you won't get much volume. If you are careful, you can make custom vacuum chucks for each part you build, that maintains the vacuum inside the part boundaries. I often use O-rings (BUNA) or 1/4" closed-cell foam weather-stripping tape for sealing.
If you are expecting to be able to mill around a general matrix pull-down table, I think you might be disappointed. The first time you open a hole, vacuum will be lost, and the part will move.
My plan is to use 1.5" feeders to each block of four square feet of table space, manifolded back to a pair of 6" ducts, that will go to a two or three horse blower (for a 5x10 table).
The problem with the blowers is that they rarely get over 5psi of pressure (according to the published curves) where my small "pucka-pucka" vacuum pump will pull 12 psi or better, but for extremely low volumes.
The research I did indicated that the big production houses used about a HP per square foot for high-volume hold-down. I was recommended a 50hp as a "good place to be", and a 100hp if I never wanted to have any issues with it.
Zeph