Sandy,
Any early fertilization you do is mainly to get the plant growing. After the first month, your vines should be doing well.
For healthy gourds, an extra dose of potash will help.
As for the seed, if you have planted the apple gourds 3-5 miles from any other gourds, and if you hand pollenate them, you will very likely have pure apple gourd seed.
Otherwise, you should plan to buy new apple gourd seed again next year.
Its easy to harvest seed, just choose a nice gourd from the gourd patch while the gourds are still green.(this is now called a sacrificial gourd). Cut it open and remove the seed. Separate the seed from any pulp, etc. and let the seeds dry on a newspaper. Then store in plastic bags in the freezer for next year.
Jan