Calculating for BIAB plus....

Hey all. After the success of my BIAB kit from brewers best, I feel confident enough that I can now make a recipe from Brewing Classic Styles. I have a couple questions though....

All of their recipes call for 7 gallon boil. How do I calculate how much extra grain and extract I'll need for a 3.5 gal boil? Is it just double? Is the time steeping and boiling the same?

I'm torn between the Dunkelweizen and the Oatmeal Stout. If I do the Stout, when it calls for oat flakes, is that the same as rolled oats or oatmeal? I was thinking of adding some flair by doing it with apple cinnamon oatmeal.

Thanks in advance for the help!

If you've done a BIAB you have an idea of how much you boil off in the hour. That amount will stay the same if you do a 3.5 gallon or if you do a 5 gallon. It's you, your stove, and the boil you have. It takes the same time to steep or mash regardless of how much you do, so even if you were doing 100 gallon batches it would take the same amount of time.

Oatmeal is flaked oats. I buy mine at the grocery store because I use them for other cooking. If I only wanted 4 ounces I would buy them from the LHBS.

Oh, if the recipe you are looking at has a 7 gallon boil for a 5 gallon batch (normal) you would reduce the amount of grains for the smaller batch, not double them.

I'm sorry, I may have been unclear. I don't have the ability to do a 7 gallon boil. I can do a 3.5 gallon boil. I still ultimately want the 5 gallon batch