Looking at Girardi as Yankees manager we can gauge how he used the DH; below are his three most common DHs by year and their games:
2008: Matsui 66, Damon 27, Giambi 26
2009: Matsui 118, no one else more than 10 games
2010: Thames 41, Posada 30, Berkman 25
2011: Posada 90, Jones 16, Montero 14
2012: Rodriguez 38, Ibanez 28, Jeter 25
2013: Hafner 72, Wells 22, Rodriguez 16
2014: Beltran 76, Soriano 25, Jeter 15
2015: Rodriguez 136, Beltran 8
2016: Rodriguez 57, Beltran 34, McCann 32
2017: Holliday 90, Sanchez 18, Headley 14
So it looks like he was not predictable in the way he employed the DH ABs. He had a couple of substantially regular DHs in Matsui and Rodriguez; sometimes used the spot to get the ABs for his catcher; and seemed to, on most occasions, try to max out one guy at about half the games. Almost all the DH ABs went to older players.
Also, there was lots of year-to-year turnover in DH ABs. I'd say he was very flexible in how he used the position from year-to-year.
If I had to predict I'd think he would use a couple of guys pretty regularly (Bruce, Cutch?), get Realmuto about a game per week DHing, and be reluctant to use Bohm at the position (he's never had a young DH with the exception of Jesus Montero, whom he used very sparingly in 2011 after he came up.).