Rusty, Yep, step one is get the threadless headset with the bearings get a dog bone that will fit your handlebars and the 1/1/8 tube. Also don't forget to make sure you have the fork tube spine nut that gets pounded in about 1/2 " down the tube after its cut. Once your headset is installed with bearings and any optional spacers and then dogbone for your preference height. It just get all manually pushed together so everything is seated then measure and mark with a sharpie just at the top of the dog bone as your cut will be like a 1/4 inch below that line as it gives it slack to be tightened down using the top ufo shaped washer that has a allen head screw that threads into the spline nut. Tighten up the UFO washer as it pushes against the dogbone. This sets your preferred bearing tightness.
when you cut your down tube use a cheap hacksaw or a dremel with the cut off saw blade. make a straight cut is my only advice on cutting. Just enjoy the learning curve as I was in the same boat not messing with bikes in 40 years but you will love your GT2A for so many reasons. Trust me you will love the threadless system plus that Sunlit fork you bought is stellar and is my favorite, if you need photos or parts pictures or links I can get those done tonight for you, sorry for the delay on response but we had severe storm damage to my house and thousands of houses sunday morn and we are all in clean up mode still with.broken windows, roof damage, trees down and everybody's house looks like it was shot up with a machine gun from huge hail and high winds.