Melon Slice
The rear solid axle can be exchanged for a hollow axle, allowing for use of a quick-release skewer. Be mindful that the rear dropout spacing is either 130 or 135 mm, so you'll have to either remove the cassette from the freewheel and run it that way, or pick up a 110 mm wheel, install the 135 mm hollow axle and use spacers to allow the wheel to be secured in the dropout.
Painting the kit should be fine, but perhaps you'll want to leave the slider portion of the top tube as is, or least the portion that will slide into the top tube.
Good luck with the build. There won't be many more coming along.
Chris