If I understand, the only purpose of the static IP or FusionHub, is so your remote users can access the PBX. You can do that without a static IP with a dynamic DNS provider such as DynDNS.org. Peplink makes implementing such systems easy. Although I have static external IP’s at work, I have a Peplink One router at home, on dynamic IP. I can connect to it easily using DynDNS. You create an account with Dyn (or other similar) and set up that account in your Peplink Balance. Dyn and the Balance maintain a connection. The external user simply uses the domain name you chose at Dyn, and the connection back to your Balance is made.
Not sure you’ve said why you need FusionHub or AWS. Are you using AWS for server or storage?
If you really want a static IP for inbound remote access, you can get both the 1000/50 and 150/20. The remote users are initiating an inbound connection, not outbound, so there won’t be outbound rules needed. That said in my experience Asterisk (if you are using that) doesn’t do well with its external IP changing, so you should set a priority rule that all outbound from the PBX goes through the static IP WAN.
Again assuming you’re doing SIP for the PBX, I suggest you experiment with running that over LTE. In my experience the call quality won’t be consistent.