1) My gasoline drum (soon to be diesel drum) is steel with some type of painted lining. It has been fine for the past 20 years or so.
I have temporarily used plastic drums for some diesel that I acquired for free, and yes, they don't do so well with the weight of a pump.
2) I fill through the small threaded port with a large funnel
3) I assume the pump does vent while pumping. I have never vented the drum while pumping, and don't notice a vacuum that has any consequence.
4) I do not vent my drum, as it is stored in a shed and not exposed to drastic temperature swings.
5) I have a chart and 1/2" PVC pipe that I stick the drum with.
6) Harbour Freight makes a drum Dollie that I use. I also have a scissor type grabber, but rarely use it.
7) I like to buy reasonable quality tools and gear. I have a GPI manual pump and an auto shutoff nozzle, which have been very reliable and easy enough to use.