I think the f4-plan is doomed to fail. It would be beautiful if we could achieve it in good conditions, however, as you pointed out, f4 is met with ...exf4 followed by probably ...Qe7 and Nd7-e5. We get rid of the pressure on the 'a' file though, so it's better than doing nothing.
If we went for g3, preparing for gxf4 after f4, our effort will be met by ...f5! shattering our dreams.
It would be interesting to try to put our light-squared bishop on a4, but I don't see it working either after 1.Qd3 Nd7 2.Bb5 and now even Nb6 does fine
For those reasons, I think the best answer here is to immediately play c3!? It's true that Black has ...Ra2, but after Qe1 I don't really think it does much. If Black captured on c3, our queen would be now in a great square to fight for the a file. If Black does NOT capture, then we can begin to put some pressure on b4