Nothing wrong with that recipe.
If you want to read about just Alt, I can highly recommend Horst Dornbusch's "Altbier: History, Brewing Techniques, Recipes (Classic Beer Style) "
And you will see that Alt is all over the place in recipe terms. Some have wheat, some are very dark, some are higher in alcohol than others.
Removing the Crystal 80L and replacing with a Caramunich of around 75L would also be appropriate. As would using a Carafa malt of around 450L instead of the chocolate.
Some things I do not own: hydrometer, wort chiller.
Some things I do own: 2 stainless steel conical fermenters, stainless brewpot with welded ports for ball valve and thermometer, refractometer.