Starting with the plus or minus question; the minus pin gauges are slightly
smaller than their marked diameter (usually by about .0002") so if a minus gauge fits and the next larger diameter doesn't - you know the hole falls within those tolerances. If you have both the plus and minus gauges you can use them as a go/ no go set with a known tolerance of about .0002".
In common practice that level of tolerance isn't needed and just the minus gauges will get you within the range you need. If the minus gauge just fits and the next larger minus gauge doesn't fit, you are within the difference between the gauges, usually about .001" ; AND THAT'S GOOD ENOUGH
Now for the number of pins. A 44 caliper revolver is dealing with the diameter of .429" but then we get into groove diameter, bore diameter, throat diameter and we need to have enough pins to measure the possible diameters involved. Obviously we can't measure groove diameter with pin gauges but we can measure throats and bore diameters. The SAAMI specs for the 44 Special throat is .4325" and the bore diameter spec is .417".
So using that as a starting point and only needing gauges for the throats; I would say that a set of minus gauges starting at .428" and going up to .434" should cover your needs. If you want to get pin gauges to measure the bore, you're going to need to add a few more pins to get down to .417"
Personally I would just slug the bore and measure the slug with a micrometer (which gives you the groove diameter not the bore diameter).
Hope that helps.