Yes, yes, and yes.
I prefer Krylon but try a few brands and find out what you prefer.
Sometimes they last for years, but after a month or two from first use they 'll be questionable.
Yes, they need to be shaken for at least a full minute after sitting for an y appreciable period of time, and periodically during use.
Also after use spray while holding the can upside down to clear the nozzle until it sprays clear. If the nozzle clogs anyway you might be able to fix it with your thumbnail - clear the slot in the stem that pushes down into the can. If it's still clogged you can soak it in some paint thinner/aceto ne whatever to try to save it.
I also save old nozzles that still work when I use the end of a can, just i n case one clogs up unsalvageably in the middle of a job.
nate