For every 2 cups water you need half cup of dme.
1l ~ 1qt in my book so just add slightley less than a cup of dme
You can basically use anything you want to make a starter in just as long as its clean and has something covering the top so dust and junk doesn't fall in, most people on here use foil. If you desire i see no reason why you couldn't make 2 smaller ones then just mix them together if you like but personally I would just use a smaller pot with a lid or a growler or 1 gallon jug... or anything that holds it all.
And since its your first time, remember to chill the wort you make for you starter just like you would your beer so you don't kill your yeasties