Mash Bill

Don’t over-think your grain when making your mash bill, obviously, there are different styles based on the grain but grain only contributes about 20 to 30% to the flavour. Your yeast selection and distillation choices, as well as ageing, can reduce that flavour contribution further. For example, having a meticulously curated grain bill, and then running extremely sharp cuts will remove any flavour nuances, having sloppy cuts will introduce a wide range of flavours, some good some bad. The grain is important for the style, but through the distillation process, you will be stripping a lot of those flavours away, so do some experimenting and then stick with whatever you have found to work for you.

And it should go without saying that if you are making rye, malt or other straight grain whisky then your mash bill will be pretty simple.

Almost every combination of corn, rye, wheat and barley has been crafted into a whisky at this point. Unless you are trying to incorporate different grains, like spelt, don’t spend too much time on your mash bill. Your choices should involve making a whisky you like and then factoring in cost and ease of production.
https://modernthirst.com/home/bourbon-whiskey-mash-bills/

It should be noted that certain grains like rye and oats can make for a really sticky mash—think cooked oatmeal—that is hard to extract the sugars from during sparging. Barely and wheat are popular because they don’t form glutinous blobs during mashing making sugar extraction relatively easy. Each grain has its place but if you are new to distilling it might not be the best decision to make an oat grain whisky to start.

And you don’t need to use all malted grains, you can if you want, but it can be a bit more costly and less environmentally friendly. Usually 5% to 10% barley malt is sufficient to convert all the starch in unmalted grains.