I think Athos is right, the wiki claims the third Kazekage learned his iron style by watching a previous Jinch (who obviously wasn't Gaara) and the wiki claims that really old dude could use sand, although that doesn't have a footnote, so take that one with a grain of salt.
As for Tomi's initial claim, and just my opinion on the matter and not authority as a council member
1. Passive abilities:
You get to keep them, although I do recall a thread where people complained and wanted a limit on this. As the complaint was people didn't want a user to gain access to multiple elements. Like Mastering the Ichibi, Yonbi, and Gobi and claiming sand release, Lava, and Steam. There was no official rule, but if you want to be extra safe, I'd say pick between Yoton and Ink, but not both. But you do you, just a suggestion.
2. Normally in the past, if one had full mastery of the beast when they got it back they could claim full mastery.
But if you guys want these to be included in the actual rules, once the biju council is up and running, and enough people want them explicably stated, the community can forward it to the council.