Sounds like you have a pond that leans on the bass heavy side. IE, your bass are a bit too over abundant.
Is there any submerged aquatic vegetation in the pond?
I see no reason why adding YP and WE would be an issue. However, if you have 2 and 3 pound LMB, you will need to stock larger WE to give them a better chance of surviving to a harvestable size. YP often struggle to maintain their numbers in a pond with abundant LMB if there is limited submerged vegetation.
I'd skip the crappies.
Another species to consider for diversity which may work quite well in your pond would be HSB.
