rfl.
Firstly welcome to our friendly forum, secondly, if you lot keep bringing out group 2 Escorts I'm gonna have to get that GAA Capri I've been promising myself!
As to your questions I can only refer you to the regs which dictate tyres etc. Wheels will have to be as homologated so for the Mk1 13" it is, but you can use Group 4 rims so that should give you the width.
You will have to run on Dunlop M section tyres because you are running in Group 2, only Group 1 runs on the D83/84.
I'm reading from the April 2006 edition of Classic Ford and there's a feature on the twink which currently runs in Groovy Baby. Mind you I didn't think Ford homologated a five speed box for the car (perhaps someone can check?) so if the article is true it looks like somebody else might be flexing the rules somewhat.
Good luck with your project and if all goes well for me I'll get out with you at some point in the season.