Are the Prodrive,
WRC, door cars not shaped around the cage? If so, I would get them before the cage or else they may not fit. You also have to consider if you need/want a full
WRC spec cage or if it will be up to the regs for what you intend to use the car for.
Also, once it is caged..... it will never be the same and I predict that you will go down the path of others... and get sick of it.
I hope this doesn't happen as you have taken the project this far, I just hope you start enjoying it soon.
Can not wait to see the finished product