Sounds like you have things about right, although I've never sparged by moving grains in a bag from one pot to another. I think your OG would definitely be low if you did a no-sparge. What is your typically efficiency mashing with that technique? I wouldn't worry about doing a mashout, it'll...
I'm not an extract brewer, but Beersmith converts 9 lbs of 2-row (65% eff) to 5 lbs of DME, so I think you definitely need more fermentables. I'd recommend more 2-row, but it depends on if you have the capacity to mash that much.
If you don't have a brewing program, I highly recommend it...
I'd probably go w/ a couple pkts of dry yeast (maybe Notty?) instead of more liquid yeast. Yeast count should be higher that way. I'd also suggest keeping the fermenter agitated - swirl, not aerate - to help keep the yeast suspended and active.
Who knows. You definitely don't need 2 pkgs of yeast for a 5 gal batch if the yeast is good and pitched properly. Maybe they put 2 in there in case one doesn't take off - happens sometimes.
You need the barley, because it has the enzymes needed to convert the oat's starch to sugar. The barley won't affect the flavor, since it's the same as your base extract, you'll just need to use less extract since the barley will add fermentable sugars. That's where a brewing program comes in...