I am not going to make any predictions on these locomotives, or try to speak for the Steam Department. The three active shop projects are the 1630, the 5, and the 428.
The 1603 will get firebox repairs and it is unknown how extensive that job will turn out to be. More testing is needed. New tubes are needed.
The 5 has all tubes out for their replacement, including superheater tubes. The trucks need spring repair, and some bad staybolts have been found. With a conventional engine, staybolt replacement would be much simpler, but the boiler on the shay fits inside large steel frame beams so the offending staybolts cannot be accessed without lifting the entire boiler out of that frame to provide access.
The 428 has been an active project for many years, and a lot of the 'heavy work' on the boiler has been done and done well. Next is the running gear, wheels, main wheel bearings and that is underway. There is also work being done to the cab to repair it, and eventually re-mount it to the locomotive.
More workers could speed the process, and more donations and money might allow hiring of some of the work to speed us along the timeline. Right now, those are not options, and the Steam Department is doing a lot of technical and complex work. Essentially they are working, in some cases, with an empty bag of chicken feathers for their resources. All of the above mainly status and my personal opinions.
To even guess at that answer would be very difficult, and realize that is me speaking as an IRM member, in no way projecting plans for the Steam Department.
If the three active projects being done now all reach the operating stage, that would be pretty much a full workload, both to keep them in running order, going through mandated inspections and tube time, etc.
THREE is somewhat a magic number as evidenced by other preservation organizations with that goal, and still a big challenge to do even that, even with paid staff.
Large engines like the 3007 may be a fan favorite but they are not really appropriate to our line and operation, and small engines like an 0-4-0 would not have the muscle to pull even a short one of our trains.
Priorities can and should evolve as needs and resources become available. For instance if someone sent in a wheelbarrow of money for a single favorite engine of theirs, we would certainly have to consider and change plans.
If a major defect were uncovered that made restoration impossible then another candidate might move up in the cue.