Custom lines are for when you finish IOE-assuming you finish IOE after the bid closes for your new seat.
Haven't transitioned seat positions under the new contract. But, best thing to do with the old was to bid for a line w/flying after the beginning of your training. EG-everything after 14 Sept.
You don't get X-CH for every day of training. All you get is your BLG. And, you only get paid carry over for the trips you actually fly-EG, the carry-over trip (or M/U trip) you did prior to the 14th.
In the midst of training, you do need to pay attention to what you are bidding. If you just bid highest paying line, you could screw yourself out of some buckage. You need to take the time to figure out the lines paying higher than RLG and VTO and bid those to maximize your compensation for the joys of multiple days in the school house.