Don't forget the dishwasher drain hose needs to make a loop up high between the sink and the wall before coming back down to join the new disposal.
Currently, that hose, pictured going to the broken garbage disposal below, is just a short straight rubber hose.
Does that hose need to be replaced with a longer hose so a loop can be made? If so, would that be a vertical loop or horizontal one? Also, what is the function of such a loop? If it's supposed to be oriented vertically, it seems like it will act similarly to a P-trap and will always hold some waste. Is that okay with a rubber hose?
If it is relevant, that dishwasher does have an air gap.
As an aside, you can see what appears to be either discoloration of the hose or some sort of coating. Is the color variation an indication that the hose requires replacement? I think the hose is probably about 10-15 years old.