With the present personnel, here's how I would aim to parcel things out among the non-catchers, rounded to a 160-game season for simplicity, and with the understanding that injuries inevitably blow these things up:
By Position
DH: 70 games from Yoshida, 20 games from Devers, 20 games from Abreu/Dalbec, 10 games from Casas, 20 games from Story, 5 games from O'Neill, 5 games from Duran, 10 games from Grissom.
LF: 70 games from Yoshida, 70 games from Duran, 20 games from Refsnyder.
CF: 65 games from O'Neill, 65 games from Duran, 30 games from Rafaela.
RF: 70 games from O'Neill, 50 games from Rafaela, 30 games from Abreu, 10 games from Refsnyder.
3B: 140 games from Devers, 10 from games from Dalbec, 10 games from Reyes.
1B: 140 games from Casas, 20 from games from Dalbec.
SS: 120 games from Story, 30 games from Rafaela, 10 games from Reyes.
2B: 140 games from Grissom, 20 games from Rafaela.
By Player
Devers: 160 games, 140 at 3B, 20 at DH.
Casas: 150 games, 140 at 1B, 10 at DH.
Grissom: 140 games, 130 at 2B, 10 at DH.
Yoshida: 140 games, 80 at DH, 60 in LF. Set things up so that he DHs ~2/3 of his games on on the road, and plays LF ~2/3 of his games at Fenway.
Story: 140 games, 120 at SS, 20 at DH.
O'Neill: 140 games, 70 in RF, 65 in CF, 5 at DH.
Duran: 140 games, 70 in LF, 65 in CF, 5 at DH.
Rafaela: 130 games, 50 in RF, 30 in CF, 30 at SS, 20 at 2B.
Reyes: 50 games, 20 at 2B, 20 at 1B, 10 at 3B, 10 at SS.
Refsnyder: 30 games, 20 in LF, 10 in RF.
The Abreu/Dalbec Roster Spot: 70 games, 30 in RF, 20 at DH, 10 at 3B, 10 at 1B. If everyone's healthy, one of these guys is in Worcester at any given time.
The disposition of the Abreu/Dalbec roster spot may occasionally press Refsnyder into a few 1B/DH innings or Grissom or Rafaela into a few frames at 3B. The goal here is to give everyone ample time off except Devers and Casas, which will hopefully keep some of our durability question marks (e.g. Yoshida, Story, and O'Neill) at peak performance.
We could add another RH bat if a good one fit the budget, but it would come at the cost of playing time for Rafaela, principally. So I would decide on that on the basis of what we think about his development. If we want him to get another few months in AAA, then sure: ink Tommy Pham or Adam Duvall. If we want to reap the rewards of Rafaela's defensive play from April on, on the reasoning that he doesn't have a ton to prove in AAA (after all, he hit .302/.349/.520 with a 21% K rate in 485 PA in AAA last year), then we're probably set, at least pending a trade.