You are seat locked into the aircraft that you are hired in, and you are correct that it is "right seat to right seat". Meaning that if you are hired on the EMB120, you must wait one year from your DOH before you will be allowed to transition to the CRJ (or ERJ as well now). If somehow there is no one senior to you bidding for a particular captain slot (base and seat), you are allowed to upgrade prior to your one year seat lock being up, but this is NOT going to happen anytime soon, though it has occurred as recently as 2007.

Starting off in a different aircraft (EMB) doesn't get you to another one (CRJ) faster, except that seniority is strictly DOH, regardless of aircraft, and CURRENTLY the only new-hire classes that are being run are for the EMB. Therefore, even if you wait until the magical CRJ new-hire class, everyone who took the EMB before you will be senior to you and after a year will transition over and bump you down in your base, and be ahead of you when upgrade time rolls around. Some may not see this as an issue, but ask the guys still waiting to upgrade after 7 years if they'd have traded a few months' seniority for being hired directly into the jet. As always, YMMV.