Use a primer that states it will stick to galvanized steel.
Zinsser water based cover stain will stick to galvanized metal, according to the label, and I have used it for such. It is made to stick to glossy and smooth surfaces without sanding. Some of the Zinsser primers stick to tile and glass as well. I used the oil based cover stain all the time, before they came out with a water based version. Bullseye 123 primer is also by Zinsser as well as BIN primer. They are all very good, but have different purposes.
Kilz *****, in my professional opinion, and is pushed by home depot. On the kilz products sold at HD, it said to sand glossy surfaces first. Originally, I bought the zinsser primer at the local paint supplier that we used for many years and then the Sinclair and ICI paint stores.
With all that said, I never had a chance to prime galvanized and go back years later to see how it held up. It is very common to see paint fail to adhere to galvanized material, but it is usually outside and often I saw the failure on trash enclosure gates. They got beat up and who knows if they were primed properly. When I had to paint them, I had our cleaning crew go by and hit them with the pressure washer and alkaline soap. The water temp was set at 200+ degrees on those units, so it cut through all the grease. After I cleaned up any left over peeling paint, I primed with zinsser and painted the gates again.
On the ceiling, I would make sure it is clean (probably a pain to do) and then spray it with an airless and cover stain, then a good white paint. It shouldn't see much abuse on the ceiling and flat is forgiving as long as you don't have to try and clean something off it.
I don't know if the concrete will cause any issues, but I would make sure the temperature of the metal and air is warm for a day before you paint and that it stays that way for a day afterwards. The concrete may be quite cold and it could hold moisture. This seems like a job for the warmer months, unless your garage and the area above stay at a decent temperature.
Primer is always better than paint, in my experience. I would rather use great primer and two coats of it, then middle of the road paint, than just an all in one paint that is expensive. Now, there are direct to metal products out there and my uncle (a pro painter also) has commented on how well they worked, but I don't know if they are made to go over galvanized. It was a pro grade product and not something like the HD Behr Ultra or Marquee. The ultra was good when it first came out, as a primer, but in later years it has sucked. I can't see paying $45 a gallon before discount for their paint, so I haven't used it.
