First (and I'm not joking) Williams needs to beat out Funk for an RB3 role. Jourdan has hinted before that the Rams viewed an expanded role for Funk in his 2nd year. And whoever is the RB3- above all- needs to be a special teams contributor first and foremost.
That said, I think the Rams could easily use three RBs in a rotation. That could change week to week. And of course health is a factor. The RB3 could become a RB2 at any time if there is an injury.
But I think Akers, Henderson and Williams/Funk could all rotate in and contribute. That might evolve as the season progresses. But Akers can pound the rock between the tackles. Henderson is a quality RB who can catch the ball. Williams is a good pass blocker and receiver. I don't think it is any sort of either/or scenario at RB.