16 pounds of apples will yield about 1 gallon of cider. For a 5 gallon batch of cider will need roughly 80 pounds of apples. Since you are looking to do a 20 gallon batch you will need around 65 pounds of apples- you will need to press to extract the juice.
I’ve only made 100% rye whiskey in 5 gallon batches- I used 15 pounds of Rye Malt in that batch- it came out great:http://beveragecommander.com/blogs/beverage-commander-blog/14166207-100-rye-whiskey-moonshine-mash-recipe
If I were going to make an apple/rye mash I would do something like this:
75% apples
25% Rye
55 pounds of apples pressed and juiced
15 pounds of Malted Rye (make sure it is malted)
Mash the malted grains for 60 minutes at 150F (use the brew in the bag method if needed)
Add enough water to get 21 gallons of total volume (for trub loss)
Take a hydrometer reading and add sugar until you reach a starting gravity around 1.065
yeast of choice