Apologies in delayed response. I checked with internal team on your ask.
We foresee in our reference architecture the usage of separate ILBs for the DBMS layer and the ASCS/SCS layer. Related to Webdispatcher it depends on the SAP release and whether you can use the build-in WD of the ASCS/SCS as this should work with more recent NetWeaver or S/4HANA stacks. Also be aware that there are some considerations around the Standard SKU of the ILB which re documented here.
As of the pricing, you check on our price calculator how things work: Pricing Calculator. When you start using it, it is obvious that the each instances of the ILB is charged separately.
Hope this helps.
Please 'Accept as answer' if it helped, so that it can help others in the community looking for help on similar topics.