I did this model years ago as an eight or nine stall roundhouse. Let’s just say the building and particularly the doors are a major PITA. But, it’s all very doable, especially if they structure is off the layout and you have easy access. As I recall, the protrusions from the doors slot into the recessed areas on the door frames. It’s no more complicated than that. Getting them to fit properly is another matter. What I’ve done (and re-done a few times when I’ve inadvertently knocked them off working on ballasting track going into the roundhouse) is to use CA medium density glue on the protrusions, put the door in place (i.e. open), then spray with in instant cure while you’re holding the door as you want it (i.e. I assume in the open position). If you have a bit more patience, I’d use Aileens Tacky Glue, wait a few minutes for it to start curing, then hold in place until it’s firm enough to let go. Last solution would be 5 minute epoxy.
If I understand what you bought from Altoona, those pins are for when a door and the door frame have cylindrical protrusions with small holes in them to fit the pins. That way the doors can swing on the pins and are “operable.” The strap devices you have are usually for warehouse doors where the door and the wall frame are flat and even with each other. The straps go half on the door and half on the frame/wall. Not sure what those fork devices are.
I’d take some pics to help you out but, I’m out of the country right now. It’s pretty straightforward and hopefully the descriptions will get you through it. Good luck.
