If we add Santander and Garcia to the guys you mentioned, going into a playoff series we're looking at something like:
rf lukes
dh springer
1b vlad
ss bo
3b barger
c kirk
lf santander
cf varsho
2b giminez
If we're facing a lefty, Clement plays third and barger is in right.
First two bench spots are easy, Heineman and Ernie. And then you've gotta pick (likely) three of Straw/Schneider/France/Loperfido, if we go 14-12. Decent chance France is trash and makes it easy, but if he hits decently well, I think both him and Schneider are kinda redundant, and you need to pick one.
Sure, having two right-handed pinch hitting options would be nice if you're facing a brutal lefty reliever in the varsho-giminez-lukes part of the order, but I think the other guys bring more to the table.
Straw's baserunning/speed is obviously an asset and bringing him in for D for a guy like Santander would be extremely comforting as well.
And Loperfido, if he keeps playing the way he is beyond this tiny sample (high BABIP and all), he's the kinda guy who gives you a little bit of everything. You're ok with him in either corner (I was mildly surprised to learn he hasn't spent any time in cf this year), he can run a bit and has a little pop of his own. The only thing is, he's the least likely to come in and be sent to the plate in a big spot, just because all of our best hitters are righties, and maybe not having a specialty like the other guys is what keeps him off the roster.
As for the starters, ideally Beiber looks like himself, and then you've got the Beibs, Gausman, and whichever two of Berrios/Bassitt/Scherzer/Lauer are throwing the best when the playoffs hit.
Which leaves eight guys in the pen
Hoffman
Dominguez
Rodriguez
Garcia
Fisher
Varland
Little
And....probably one of the other two starters as a long man.
Edit: I just realized you didn't say PLAYOFF roster. I guess we gotta get there first.