1. Do affixes have different rarities or is it ... >> Affixes are weighted on item drop pools based on what the "stipulated" zone level is. So if u need a lvl 25 affix, I'd say u need to farm late Act 2. Now since Unyielding will only drop from formicids, devs add a lower weight to affixes from earlier zones on such an MI.
2. "Of focus" i could only spot 2 items in my vaults & both were helms, dunno if it's supposed to drop on shields but I have seen "of concentration" a LOT on vendor staffs megara to delphi normal, so hit megara to delphi epic vendors to check maybe.
3. Green/yellow jewellery does not drop from bosses routinely, more from chests. Massbosses bumps equipped green drops so that's also not viable at bosses. In my personal observation, birds (harpies, crows etc) drop more jewellery than other mobs.
If you're getting blocked on progression, u may wanna try either Blacksmith tool or MI shop mod, smithy tool is VERY VERY limited in what u can get from it but MI vendor mod is harder to get & deploy these days.