Great advice. After modifying and advancing (still a noob) skills over 7 pistols - I am finally doing a full project pistol. STILL using a frame and slide from a complete pistol but tightening it up and adding beavertail, barrel fitting, etc.
For the most part you assemble ARs from a pile-o-parts. 1911s are different. For it to be worth your time your parts will be oversized and require fitting to get the best outcome. Otherwise just buy a good quality complete basic pistol and modify it once you figure out what you want it t do.