Hi Venk,
I wouldn't get too worried about the 2mm difference at this stage. See how the tub comes together, and then either sand back or adjust accordingly.
The side panel extension pieces butt up against the rear panel, and (on mine) are about 5mm short of the bulkhead / windscreen vent panel.
This turned out to be fortunate, as the nuts for the 'windscreen hinge' ironwork would have fouled otherwise.
Now that you have the major holes in place you should be able to proceed again, as the side extension piece can be altered when it's ready for installation.
As for the metalwork for the dummy door handles, I'm sure your buddy will do a fine job.
I can't remember how I made mine, I think I bent them around a wheel hub or something similar. I have cut the door opening out completely and screwed the handles to the inside of the panel....

I added a little detail in the form of the lock barrel in the top corner. This was made from a 12mm long piece of 20mm dowel which was screwed to the door panel from the inside.
The back of the handle is hidden on the inside by a dummy door panel....

cut to the size of the door and painted satin black.
The metal trim around my filler cap / rear lights etc were made when funds were low and I needed something to occupy myself.
Keep going, you'll get there eventually,
Regards,
Mark.