Quick question - can one bestow (i.e. Hopeful Eidolon) onto creature that has “Protection from creatures” (i.e. Teysa, Envoy of Ghosts).

Yes, you can bestow onto Teysa (or any other permanent with protection from creatures). Although protection from creatures prevents targeting by creature cards or by abilities whose sources are creature cards, regardless of the zone they're in, a card cast via bestow is not a creature spell at the time its target is chosen. Since bestow is an alternative cost, the choice to cast the spell for its bestow cost happens in the second step of the casting process, at which point the card becomes a noncreature Aura spell, and the choice of target occurs afterward in the third step of casting.

Daniel Kitachewsky
L4, Paris, France
Rules NetRep