As I've mentioned on another thread, I've been out a year now so apologies if anything has been superseded.
A Military Plant Foreman is essentially the highest level of plant specialist in the Corps. By plant (if you're not that up on it), it means construction vehicles, ancillaries and equipment not mechanical/electrical services. They have design, management and logistic responsibilities and are generally found at Regt level, or Sqn in some support units.
To get there, it's best if you trade as a Plant Operator Mechanic (POM), qualifying as an A2. You will over the next few years also need to qualify as an A1 and Plant Sect Comd. The most important thing is to pick up recommendations for MPF training on these courses and SJARs. If memory serves, each year applications for MPF training are requested by RSME and those with suitable quals/recommendations can apply (most applicants will be Cpls/Sgts). The course itself is technically/academically challenging and over a lengthy period at Chatham.
Like all the technical trades, it's an excellent tick in the box for civvy street; when I was an OC, my MPF had an HND in Civil Engineering that he was working on to up-rate to a degree. It also should not limit your employment in Regt. The same MPF was ranked the best staffie in the Regt and picked up first look.
Something to consider is that there was talk, I don't know how idle, to change the MPF to a Clerk of Works (Horizontal Construction) stream. At present, there is no accelerated promotion as with CoW.
My view, for what it's worth, is that it's the only way to go with C-Veh PFI. The traditional role of the non-MPF Plant Sgt in terms of fleet management, etc will fade away as fewer vehicles are kept in units.