Update: this information can be found in other Posts, but I wanted to test whether having different Difficulty Settings between Main and Hireling affected anything.
Ascending Build: this is a build used to get the Experience you need to get Perks. it takes a lot of Experience to get Perks, the more Perks, the more Experience you need. what makes this build different from others is eventually you will have 6 Quest Stones on it to get the +200% Experience cap. as I was testing, I noticed that my Main and Hireling both had a +50% Experience Bonus. they are both at the same level when I looked. I know that when the Main and Hireling are different levels, that bonus gets reduced. when I had a level 99 Main leveling a level 1 Hireling, the Hireling had a .4% Experience Bonus. another thing I tested was do they average out the Experience Boosts from affixes. yes and no. I didn’t test out the Legend Experience affix, but I did use a Quest Stone. I put a +30% on my Hireling and only got +15%. but my Main didn’t get any bonus from the Hireling. I put a Quest Stone on my Main for +40% Experience and got +20% Bonus, but the Hireling only had the +15% from his Quest Stone. so Experience is averaged but not shared. it could be my device was acting up as far as this Experience experiment went. later when I craft Ascending Builds for my two Characters, I’ll update this part of the post.
Farm Build: this is a build used to get loot. some players make a Farm For Everything Build and others make a Specialized Farm Build, like a build focused on farming for Eternal Items. Gold Find affix and Greed Nature only needs to be on the Main Character. Nadroji Set and Bonus, Eternalized, Mythic, and Crystaline Sets are the same, they only need to be on the Main Character. Luck affix and Nature, and Item Drop Rate are averaged between the Main and Hireling. this also includes the bonus from the Difficulty Level. I tested my 2 Characters with M3 on both and 1 M3 and 1 Easy Difficulty, and Luck and Item Drop Rate were both affected when the Difficulty Level was different. because Gold Find is based on the Main Character, if you switch your Main and Hireling around, and the Hireling has a lower Difficulty Level than the Main when switched, then Gold Find will go down. Fortune Skill needs to be on both if used, for Luck and Item Drop, but doesn’t affect Gold Find from the Hirelings perspective. if you want, you could use Fortune Skill on Main only and just use Luck and Item Drop on Hireling to keep things even.
when using a Main and Hireling, there is a +100% Item Drop Rate over cap. so getting +200% Item Drop with Main and Hireling will give you +300% Item Drop.
Perks: for players who get those Perks, Dealer Perk is the only one that works with the Hireling, all the others are based on the Main. if you plan on having your Hireling be a permanent Hireling, then you only need Dealer Perk for it. but if you like switching your Characters around, then you get all the Perks. I think I will have my Warrior be the Hireling while Ascending for the 6 Perks, so Dealer will be first for him. Rogue will be the Main, and I think I will go Fortunate, Accomplished, Dealer, Enshrined, Hunter, Treasured.