The stretch from 125mm to 130mm is acceptable but to stretch the drops another 5mm apart, to 135mm is just too much, in my opinion. You should replace the rear hub and fit a six speed freewheel to it.
Changing brake calipers is not a big deal, provided the ones you install will reach the wheel rim braking surfaces properly. Ensure also that you get brakes that have the correct mounting system (hex head nut as opposed to socket head nut).
Forget the eight speed transmission. The drop faces will not accommodate the eight speed properly. Stick with the six speed and seek out bar end shifters. Suntour Barcons are very nice, work great and will suit the bicycle just fine.
You can take the bicycle to an automotive paint store and they will custom match the paint for you.
All that said, you seem pretty new to the interest of vintage road bicycles. I publish a website,
MY "TEN SPEEDS" with the intention of helping, like you, get a head start on the interest. A visit or two to my website just might end up saving you a good deal of cash, effort and frustration.
I hope this has been a help and welcome to the Bicycle Forum, one of the best vintage bicycle information sources on the www.