FH success mostly helps BFR in regards to operating a ton of engines simultaneously (27 for Heavy, 31 for BFR) and in operating heavy lift capacity rockets in general.

BFR/BFS will come online as a self-competitive offering from SpaceX initially and both lines will be out in the market together (BFR vs. F9/FH). If and when BFR attains sufficient maturity, reliability, and market trust then the Falcon line of rockets will be phased out. BFR will have much greater capabilities (higher payloads, etc.) but will be substantially cheaper because it'll be 100% reusable and the reusability longevity for its parts will be much higher than for F9/FH, so there won't really be much reason to keep Falcon 9 or Falcon Heavy around.

> FH success mostly helps BFR in regards to operating a ton of engines simultaneously (27 for Heavy, 31 for BFR)

However, the FH uses RP-1-O2 Merlin engines, whereas the BFR will use Methane-O2 Raptor engines, so they might not learn too much.

Edit: RP-1 fuel.

If BFR is as successful as Musk hopes (_especially_ around the reusability aspect), I think BFR would replace the F9 and Falcon Heavy as a lift vehicle.

If BFR is actually fully reusable it would be cheaper to launch than the F9 (due to the non-reused second stage).

Musk has actually said that he expects BFR to be cheaper to fly than their original Falcon 1 ... meaning prices in the $5-10M range, as opposed to $60+M for F9.

I think that was referring to cost per kg to orbit, not cost per flight.