Okay! And no the cap wasn't on tight enough. But what and where are the pressure caps? I'll clean the carbs and the VES thing again and see what happens from there and get new plugs.Stuff from the old gas getting in the carb it happens. Wait there is barely any coolant in it? Hopefully you don't have a leak anywhere so check out all hoses, water pump and what not. Green 60/40 is what Polaris uses OEM so buy a gallon of straight green and mix it 60/40. Also you will need to "burp" the system to get all the air out of it. To do that you jack the front end up as high as you can get it or put it on a hill so engine is much higher then the rear radiators. Then you take the pressure cap off and start it and let it run at idle for 15-20 minutes and very slowly the air will come out while you check the overflow bottle and what not.
Yes always keep spare spark plugs and spark plug cap ends as well. I run NGK Iridiums in mine as they last a lot longer then standard NGK plugs. Drain it with w/e pump you have, I use a amazon pump that was like 5 bucks that pulls it out with no issues.