Your diagram is too small, but here are my thoughts given what I think you're asking.
1. Certainly adding an HLT will allow you to fly sparge. Honestly, I've always fly sparged but I don't think there's much benefit from it. It takes longer and the efficiency gains aren't all that great.
2. Unless you're planning to make an extremely mild beer or if your MLT is much larger than your BK or HLT (sounds like it's a keggle, so it's not), I don't see how you could get enough grain in the mash to take advantage of two boils.