The squash start with a "heritage" variety which is self fertile (does not need bees to pollinate across multiple plants).
I am a little confused by your term self fertile relating to squash.
All varieties of squash (zucchini, crook neck, butternut, spaghetti acorn squash) that I know of have male squash blossom and a female squash blossom separately along the same vine but you definitely need some insect to visit each type of flower or you won’t be setting any squash fruit. For the sake of genetic vigor, the books recommend 12 to preferable 25 plants (not just individual fruits). Fewer and you can have genetic dwindling in a few generations. We try to plant them in hills and run 2 or 3 vines from each hill in between the vines growing from the next hill. Also many very different cultivars and actually the same species.
Field pumpkin, summer squash, and zucchini are all pepto and can interbreed and very undesirably so! The bees don't care where they have been so try to plant only species of C. moschata, C. maxima or C. pepo in the same year if you are saving seeds.