Mechs that travel as cargo are hard shut down and effectively inaccessible. This means that they can't be hot dropped and that they have to be unloaded (we have to have landed and not be under immediate attack) before they can be used. So if you are planning to work on a mech, it will have to be one of your 4 "primary" mechs. Your primary mechs are the ones in the 4 mech cubicles actually assigned to your lance. This creates the very real chance that your lance may need to drop in an undesirable configuration, based on your choices of mechs to load as cargo vs. as primary.
Dunedain Lance will be loading with Dunedain 1 (Crusader #1) in cargo while the new salvaged Crusader (#2), which just had its engine changed, has its weapons modified. My Thunderbolt, Shadow Hawk and Firestarter will round out my primary mechs. If we need to hotdrop, I will not have access to Crusader #1. If we land and are under immediate attack, I will not have access to Crusader #1. Any time after that, I will have normal access.
As for cargo mechs requiring maintenance, I would assume that either you have bored techs squeezing into the cargo bays for something to do or that hard shutdown mechs do not need appreciable maintenance. Rob, will have final say, of course.