Well, I don't know about future raws as I can only read the translations myself, but so far:
I'd say Yes for both questions. He hasn't married a concubine yet (as far as translations go), but there are direct and certain talks about it. Pretty much set in stone unless something happens. But it's not happening soon, cause it's directly linked to some political agreements which are still in the works.
Zenjiro didn't really like the whole situation, but he's gradually accepting it.
And it's definitely far from harem tropes, since polygamy here comes from political interest, and not a bunch of girls romantically falling for MC.
I'm not sure how much spoilers you want, so I'll just stop here without details.