Culture fresh buttermilk with yogurt I would like to try culturing fresh buttermilk that I get from whipping butter. I would like to ask if storebought "cultured buttermilk" is done exactly like homemade yogurt, but with fresh buttermilk?

Thus, would the methodology be as follows?

(1) heat buttermilk to simmering
(2) cool down to 110 F
(3) add live yogurt culture
(4) incubate at the proper temperature

Thanks for any insights or those who have attempted this before.
You seem to have gotten the process backwards. You don't culture the buttermilk. You culture the milk, then whip the butter, and the rest is cultured buttermilk, at least if you are going for traditional buttermilk. If you want modern buttermilk, you don't whip anything, just culture the whole milk and consume the result. 

The original method would include "self culturing", so you just leave your freshly milked milk at room temperature until it is done (soured). This is not considered acceptable by modern safety standards, even if you have your own cow. If you are starting with milk you bought somewhere, it is not even likely to work. So your best bet to get buttermilk culture is either a package of storebought buttermilk with live cultures, or to look if some specialty store sells the culture itself, possibly online. 

I cannot comment on the perfect temperature/time conditions for buttermilk, they are also likely to differ between strains just like they differ between yogurt strains. Maybe somebody else can post the usual ones in another answer.