More grain, more alcohol? In theory yes, yet this is not only dependent of the amount of grain; this also depend of the type of yeast.
This is a misleading statement. Type of yeast are generally NOT a variable in ABV for typical brews.
Stick pretty much any yeast in a typical 1.05-1.06 OG wort, and you are going to get very very close to the same ABV, all other variables being equal. Varying the type of yeast has nothing to do with ABV unless you are talking about specialized yeast with specified attenuation rates, which are typically only used in very high ABV brews or very specialized brews.
Nil, different types of grain have different enzyme qualities and carbohydrate content. The enzymes in the grain are what breaks down the carbohydrates into simple sugars that the yeast can eat, which then becomes alcohol and CO2 as the yeast byproduct. There are also many grains that don't contribute to sugar or alcohol content at all, and only contribute to your beer's color or flavor.
So, in general, more grain = higher alcohol content, but it does vary from grain to grain.
If you are trying to design a brew, a typical 5 gallon batch of average OG and alcohol content (1.05/5.5 ABV or something around there) takes about 10 lbs of fermentable grain.