1. Film holders really help, if you have some. I fit mine against weatherstripping to make a light-tight seal. You can use the darkslide on the holder to 'strip test' (ie. bracket) your first few test exposures. You will need to give the paper a small trim to fit the holders, but that's no biggie.
2. Yes, or any old yellow filter, but likely in front of the pinhole -- just to protect it from the elements. Alternately, you can shoot on overcast days when the contrast is lower, or you can pre-flash the paper a wee bit. Softer developers (diluted Selectol-Soft) are also an option.
3. For best results, the pinhole should be sized according to the so-called focal length. So for a 10" distance, you'll need a pinhole in the neighbourhood of 0.6mm.
4. If you are proceeding with a 'normal' focal length, you might want to fit a wire frame or suchlike to aim the beast.