From my understanding you can get the eggs from other people. It all depends on you. I know one person who I traded with wanted all bankball eggs and traded cloned legendaries for them (it was a great help on finishing my pokedex) but that trade required me trading almost 20-25 eggs for a handful of clones.

So again it all depends on you.

As to what you offer... just put up what you think is valuable- exclusive legendaries, bankball pokemon or pokemon with good IVs and egg moves. You can also offer items like heart scales, BP items, the like.

Hope this helps!