Starters are generally only for liquid yeast. Simply rehydrate your dry yeast as directed (I like to add in a little Go Ferm, but YMMV) and pitch. Dry yeast is so cheap that if you need a higher volume of yeast you can just buy another pack.
As for your questions above....
1) Yes, they're assuming you've made a starter of your desired gravity.
www.yeastcalc.com can tell you how much DME to add to X volume to hit Y gravity.
2) You can step up starters, but that takes additional time. Finish your 1L starter and put in fridge 24hrs then decant off most of the liquid, then warm the slurry to pitching temps. Make another starter and when wort is chilled to pitching temps add it back to the 1L flask and put it back on your stir plate. It's a PITA but doable until you buy a 2L and 5L flask.
4) I don't use dry yeast, but unless you'd need more than say 4 packets of 11g each it's probably not worth it to make a starter. According to Mr. Malty calcs up to 1.10 OG in a 6 gal batch would only need 2 packets of 11g each.
Just rehydrate, save your starters for when using liquid yeasts