Nikolay, I would like to thank you for your help and your patience with this. We are almost done with the negotiations with the ISP for the managed router. Since we are going to be doing BGP the ISP will provide us with /24 networks so there will be plenty of IP addresses. The QFX can do per-flow (per-packet) ECMP. I understand the single point of failure on the ISP side, however that is something the ISP is responsible for and not me. I also understand that setting up clustering would make this even easier but it is not a possibility right now. They might gor for an Active/Active cluster if I can't get the independent firewalls configured.
So back to my earlier post:
1. Run eBGP from SRX to ISP
2. Run iBGP internally.
3. Use ECMP on the QFX to load balance across.
Does that sound right?