Glad to be of help, troopers helping troopers is the moto.
That was a lot of work, well done but, yes theres a but, the flat screws also have a taper so they recess into the plate which makes them flush.
It's an entirely personal preference what to use and even what you can find to use, me I'm going for the tapered flat head, but at the start of my build journey I would have settled for rivets.
Go with what you are happy with, oh and remember its not permenant you can always change it later.