SkyWest uses a conversion factor for the rotor time which would allow a pilot to get hired with as little as 250 hours fixed wing time. I believe it allows a credit of 3/1 or 4/1 for the rotor time in order to meet the 1000 hour minimum. Ie 1800 hours of rotor would equate to 600 hours of fixed wing. I don't believe they'll accept anything other than fixed wing for the 100 hours multi. The multi time doesn't need to be PIC, so the time that you use towards either the ATP or Comm MEL counts. Though I don't have any experience with them you may want to check with a school like ATP. Do you have to do anything extra for the instrument rating?
Don't about "glass training" or instructor time. Many of the regional new hires haven't seen anything more sophisticated that a 30 year old Cessna or Piper.