The Princess has the most interesting background story and could see the most development. Definitely #1. The monk looks great for comedic relief if she's sassy. The elf and the priestess are tied for me. The elf gives off the ARA~ARA-Vibe.
Going off of appearance, the monk is definitely my personal favorite cause i like the hair buns and the way her eyes are drawn. The princess is definitely interesting from a story perspective, and the priestess would probably be the best choice to boost his group's effectiveness in battle depending on how many people she could buff/heal and by how much. The elf is the least interesting to me since she just seems like a cookie cutter elf, and the human hating could get annoying. Also the way her face is drawn on that page just bothers me.
i think the order of retrieval could be archer, priestess, monk, than ruined noble, it seems the most logical since the princess would probably be the hardest to convince along with the Elf but the Elf is dealing with My boi so it should be A OKAY
my prediction is the elf is actually last because she seems to be the hardest to get to. the other 3 all kinda wander so its more feasible to work any of them into the story. (princess and monk could easily just wander thru his territory in the next couple chapters, priest could go on a missionary tour (either prompted or unprompted))
my personal prediction on the order is priest -> princess -> monk -> elf
im not sure the MC has enough time to actually go to the Elf land tho. from a narrative perspective its easier to work in any of the other 3 since they have logical reason to happen to be nearby.
edit:
nvm, you were right lol, i guess 'time' or lack thereof, is just a construct for an author to do whatever they want with (even if it isnt completely logical in the circumstance)
Monk is last for sure, both in utility and military power, elf is very nice but wouldn't she be problematic diplomacy-wise? If he had some kind of semi-competent warrior with him then it would be between elf and priestess for me but since he lacks any stable warrior to protect him Princess is best first choice followed by elf (who probably can stand her ground with summoning magic in melee as well) so:
1. Princess
2. Elf = Priestess (depends on whether having an elf ally is an issue)
3. Monk