With regards to cutting 120, does a cutter need 4 blades? 3 16mm strips from the middle and the edges get cut off? I made a cutter for 35mm that works well but sounds like cutting 120 is more economical
If you want three strips, yes, you'd need four blades, 16mm apart (you could actually get 4 strips, 15.5 mm wide, which would work, but two would have edge markings that can get into your images). You'll get three 16mm strips and a pair about 7mm wide with the edge markings. I used to get my 16mm strips by cutting 127 and loading the leftover, coincidentally 16mm wide, into my Kiev cassettes. If the original film edge is toward the cassette bridge, the edge markings (which stay on the strip with that cut) will go where the cine sprockets would, so don't interfere with your images (much).
So, yes, cutting 120 is a lot more economical than cutting 35mm -- you can get just barely four Minolta reloads out of a 135-36 cassette (it's twice as long as a 120). You could get two across if you can find unperfed 35mm film in an emulsion you want to use.
Cutting 120 and using half length strips, or getting four loads out of 135-36, requires careful loading of the Minolta cassette -- the strips will be around 15 inches, where the originals were 18. The originals, however, left at least two inches of film still in the supply. You'll also see some spacing issues -- original Minolta film was apparently made from cine stock, same as 35mm for thickness. All the Minolta format cameras, as far as I know, use turns-counter advance system, with a cam to adjust the length advanced as the film builds up on the takeup spool. If you cut 120 (slightly thicker than 35mm), you may see your frame spacing increase as the film runs -- or you may see it decrease, because modern film is thinner than what was available when the Minolta 16 and 16II were designed (and the Kiev Vega was an exact copy of the 16, while the 30 and 303 were evolutions from the Vega). If your spacing is decreasing, wrap a layer of masking tape onto the spool before attaching the film -- you can adjust this, with experience, to get the spacing to remain reasonably constant through a cassette.