- Where are the most junior bases on the 175?

Ord

- Am I eligible for travel benefits on all carriers operated by the 175 or just who I operate for out of my base?

Right now just united but in 2016 you will also get delta

- Average block hours and days off for a 175 FO?

85-90 hrs a month 15-12 days off a month

- Would the CRJ be a better option for career advancement/QoL

It might.