i've done numerous custom wheel and caliper installs on various builds. 1/8" clearance is plenty- IF you've built and assembled everything correctly: axle, spacers, bearings, true rim, disc tightened down, cotter pin on axle nut, etc...
you no doubt spun it with front wheel off the ground to check during the mod. when you're confident all is good to go on this most critical assembly you can certainly roll it a few feet your garage or driveway to test the brake.
take it easy on your first test run, and if you feel or hear anything unusual when the brake is applied- assume you have a problem, pull over and check it immediately. re-check all related fasteners for the first 100 miles or so.
i've never had a problem, but one mistake with your front end could be your last one.