I think it would be best for the Cubs if Stroman didn't opt out.
I think the Cubs are in a situation that's different than the last couple of offseasons because most of their best prospects are in AAA or AA and pretty close. I think they'll go short-term on as many guys as they can, but that may just not be possible at every position. If the Cubs sign a SP longterm it will be a rotation with only 2 open spots going forward to fit Horton, Wicks, Brown, Assad, Wesneski etc. unless they go with a 6-man rotation.
Caissie, PCA, Mervis, Canario, McGeary, Murray, Horton, Wicks, Brown etc are all probably going to be in Iowa to start the year or on the MLB team. Shaw, Alcantara, and Triantos likely start the year in AA, which means they're close too and could get called in up in a pinch like Morel and Hoerner were (though less likely because of the amount of depth at AAA).
Honestly it wouldn't shock me if they didn't sign any FA for more than 2 years, unless a great deal falls into their lap that they could flip in future seasons if needed, or keep and flip one of Happ, Suzuki, Taillon etc in the future. I'd be surprised if a significant trade involving prospects doesn't happen before Opening Day, probably for a short-term player/pitcher.