Perhaps the added layer of complexity of the VPN combined with the differences of a BIG-IP in AWS are making things more challenging. Working with networking in AWS is probably much different than your on-site solution. For example, everything is routed in AWS, there is no real L2. I would recommend getting a BIG-IP test system and pool members set up in the same VPC so that you can grasp one technology change at a time. Once that solution is working, add in the VPN.
Start here:
https://support.f5.com/content/kb/en-us/products/big-ip_ltm/manuals/product/bigip-ve-setup-amazon-ec2-11-6-0/