I have a 6X7 with MUL (Mirror Lock Up), and I also have the metered prism. Right off the bat you do not need MUL, I have taken hundreds of photos with this camera, and I have only seen two blurred shots, and both of those were because of the main disadvantage of the metered prism. What is the problem? The problem is that with the metered prism you tend to adjust the camera so the shot is properly metered and not look at your speed thus you shoot at too low a shutter speed and blur your photo. My Metered prism is accurate, your actual mileage may vary.
Check your shutter speed before you shoot and the metered prism should be fine.
I stopped using a handheld meter with this camera a while ago, I still check the meter, before a day of shooting, but that is it unless I am trying to do something a handheld does better for me.
You can hand hold this camera, I have never used a tripod with it, I took a sunset photo with it resting on a table once, that was the closest it ever got to being on a tripod.
A Pentax 6X7 can only use flashbulbs connected to the FP PC jack on the camera for fill flash. People that say this camera can not do fill flash are wrong, it will do fill flash as long as there are flashbulbs (not much longer). You can not use an electronic flash at a faster speed than 1/30 second unless you get a leaf shutter that only gets you to 1/90 second.
Good luck in your quest.