I do not have answers to most of your questions but I can answer a few and give you a little more insite. I have a miller 302 EFI. I have an older model miller spool gun that I purchased new in 1988 I believe it is a spoolmatic 3. It works perfectly with no modifications on my new trailblazer. You can pick one of these older spool gun up on ebay for $300-$400. Just make sure it has the 14 pin connector. I bought mine for my millermatic 200 that I purchased at the same time as the spool gun. The everlast 250 is about the same amount of welding power as my millermatic 200. I do not have the spot time feature and have never really missed it either. Gap filling is easy with any decent mig machine. pre flow and post flow for the shielding gas would be the only things I would look for if I were to buy a new one. That said I do not need them enough to make me want to replace my present machine. If you do a lot of auto body work and or other thin metal projects it might be worth considering but I have done some auto body with mine and it was fine for the occasional project here and there.