I neither see an issue with the 20 missions nor the 100 doffs.
The resources of a Starship are limitet. Remember that a Defaint has only a crew of fifty, I already dont know where those DOFFs sleep there.
A single ship cant handle an unlimmitet amount of officers or missions.
I just kind of wish we could send DOFFs via mail... so I could eqip my alts with Doffs I dont need or are more needet there.... after all, the alts HAVE other ships!