AVD

The number of session hosts will very much depend on the load the users generate. 

It is hard to say without knowing the expected CPU/Memory/Network load for each application.

I often estimate 2-5 GB memory pr. user and often run 2-4 users pr. CPU core in the session hosts. 
So if you choose a E series SKU with 4 vCPU and 32 GB RAM, you could have 2 of those running in one host pool. But session hosts in a host pool can only be either Remote App or Full desktop, you would likely have 1 active session host in each of the 2 host pools and then use scaling plan to have the capability to start additional session hosts doing work/peak hours. 

Depending on how many hours a day you will be running your session hosts with active users on, you may want to look at reserved instance or savings plan to cost optimize your solution.