2) after a period of time (1 or 2 days?) decant?
Decant the liquor off the top of the starter just before you pitch. Try to get as much of the pale gray yeast slurry in the middle layer of trub, as opposed to the stuff above or below it.
3) don't hang on to it more than a couple weeks
Yes, but the sooner you can use it the better and keep it as cool as possible without freezing it.
4) when I do want to pitch, get it ready a couple hours in advance and if possible, goose it with a little fresh wort
More or less right. Allow the starter to slowly rise to pitching temperature before you pitch it. No need to add fresh wort, since that's what you'll be doing when you pitch it into your beer.
Also, if you've been keeping the sample in your refrigerator, be sure to spray or wipe down the exterior of the starter container, especially the neck and lips, with alcohol or other sanitizing solution. The average refrigerator is a microbial wonderland and you don't want to risk getting any of that microbiological zoo into your beer.
Finally, don't forget to aerate your wort, either just before, or just after you pitch the yeast.