Using two packs of yeast in the starter will just get you there faster. I feel like that's kind of a waste of money because the yeast in one pack will more than double in your starter. And this is just my opinion and experience but I wouldn't worry so much about your starter size I've brewed...
In my several experiences with oats (I use quick oats) using around 10% oats I have had difficulty sparging. It's not impossible but it made it more difficult, I had to stir a lot and mess with the mash to complete the sparge. With almost half oats you will be trying to sparge oatmeal. I would...
"Iron" in its more natural high carbon state is not really used much any more it is probably carbon steel. If its galvanized I don't think that's safe. But if its just steel your main problem will be it rusting fast.
A keggle us a budget friendly option if you can find one. The keg holds 15.5 gal and when you cut off the top it should be plenty big. I don't have one myself but I know a lot of people use them.
I know 1/2 bbl kegs do not have the same connections, and I'm not sure about the 1/6 ones. You can use 1 co2 tank and you'll need either a single gauge regulator and a 3 way splitter or a 3 gauge regulator. You'll need the taps and tubing and connections to hook them all together. I'm sure...
I did the exact same thing. It's such a simple thing to make idk why people pay 50 to 100 bucks for someone to put the band clamps on the tubing for them lol