I start all kit based builds the same way,if no custom work is involved I go over the body removing flash and mold marks like seperation lines and ejector pin marks. Next up is fill and sand sink marks,etc. I next do the same process with other sub assembly items for interior,chassis,engine and drive train.
The paint process is done after subassemblies are glued togeather to minimize handling. I leave all parts on the sprue untill needed(if you could see my workbench bench you would understand). I am 100% a rattle can man so a lot of small stuff is mounted on toothpicks and those clamped in spring loaded clothes pins. Do what ever works best for you.