It's rare to have a need to mount sheet blocks on the pushpit, and is done when there is no suitable deck area for them (having said that, I do like a vertical spread of deck blocks, so as to keep the parts of the sheet separate and not rubbing against each other, and you might achieve this by mounting just one block on the pushpit, the rest on deck).
Mudita has a suitable stern deck for mounting deck blocks, this is the standard place to put them, and therefore I recommend that you put them there, until such time as you have gathered enough experience with the rig to be certain that you want them somewhere else.
Without being able to see the pushpit, I can't advise whether or not it is fit to carry a sheet block, but I would doubt it, bearing in mind the size of single sail that you are planning to fit. Pushpits have generally not been designed to carry an upwards/forwards/sideways load, just the downwards/outwards load that a person is likely to put on them.
I would have to query your intention of raising the stanchions. This is a 10m yacht, not a cruise liner! 36in stanchions would need to be 1.5in diameter - all totally out of proportion with the size of boat. Bear in mind that with junk rig, you won't be going forward at sea very much, and when you do, in rough weather, you go stooped over or on hands and knees to keep your CG low. Much better value is to rig a jackstay/manrope inboard, and to use a short tether clipped to it when circumstances demand it, but otherwise to practice moving safely around the deck, using it, and other handholds, as needed.