Hi Nikhil,
After the upgrade, all EEWB fields will remain intact. These fields will be visible on GUI but they will not be visible in web UI readily. Making these fields available on web UI is just a question of quick configuration which is very easy.
All custom logic written on IC webclient BSP applications will have to be re-written in component workbench (new architecture).
IC web client profiles will not automatically be converted to business roles. All PFCG roles will remain intact but business roles have to be created manually again.