Im brewing my first brew as well (Muntons Irish Stout kit) Been in the primary for one week now. I took a hydro reading yesterday and today and it was at 21. It tasted good a bit watery but so far so good. Anyways to the point, I am planning on using plastic coke/root beer/water bottles in 2 and 1L sizes for it. I am sanitizing them very very well.
From my look on it there should be no problem using them, a bit out of norm and im sure a true beer conisour will frown on it heavily but they are cheap, can take very high pressures(no bottle bombs), easy to close. From what I read the bottles themselves will not be a problem but the used caps might. From my experience and the look of the plastic seal in the used caps they work just fine second time around. If you do want new caps most brew supply shops seem to sell them. I would replace the caps pretty often as they are cheap anyway.
I will let you know in a few weeks how well well they work, might end up with flat beer or I will end up with 2L of goodness. Im really not worried about the seal though, just make sure they are tight.