A couple questions regarding LTM 10.2.3 to 11.3 upgrade

I have been working through a version of this for the past few days. In our case I am migrating from 10.2.4 to 11.3.0, by loading the UCS from our source systems onto VEs running 10.2.4, then upgrading them to 11.3.0. This has the benefit of keeping the failover peering intact, only requiring minor fixups to the config prior to upgrading to 11.3.0.

Both times I ran this upgrade, as long as the 10.2.4 VEs successfully clustered together after loading the UCS, they successfully peered in a DSC on 11.3.0. If your ConfigSync configuration works correctly, you should not have major issues. You will need to configure network based failover if you are not using it on the source cluster. If you do not do this, I do not believe that DSC will be built correctly on the 11.3.0 instances.

One note is that prior to loading the UCS, I activate the license on the VE. When I load the UCS on the VE, I pass in the "rma" option.