We've seen this before: A great player takes time off due to injury, and comes back revived. What we saw from Federer at the AO was, in my opinion, the best he's played since at least 2012. Better than 2014 or 2015. He was less shank-prone, his forehand and backhand both were devastating, his serving was great, and his movement good.
So now it is about pacing and, as he said, staying healthy. Whether he's ranked #2 or #4 doesn't matter, but whether he's ranked in the top 4 or top 8 does, so that has to be taken into account (if not, then he might be tempted to just play Slams, the WTF, and the prep tournaments and not worry about the Masters).
So thinking that way, it makes sense or him to skip Monte Carlo and Madrid, but he's going to want some clay preparation for RG. Another thought would be one of those ATP 250s - what about Geneva? There's no gap between that and RG, but it might be a good way to prepare.
Here's the May schedule:
May 1: Estoril, Istanbul, Munich (all ATP 250)
May 8: Madrid (Masters)
May 15: Rome (Masters)
May 22: Geneva, Lyon (ATP 250)
May 29: Roland Garros
So I guess Rome really does make the most sense, in terms of timing: it is close enough to RG so that playing a few matches there will be a good warm-up, but not too close that he might be tired to start the Slam.
It is also worth considering that there's a huge gap between Miami (March 20-27) and Roland Garros (May 29) - that's two months of entirely clay tournaments. He's probably going to want to play something in that two month period, maybe one in April and one as prep for RG in May. Maybe Monte Carlo (April 17) does make sense?