Keep in mind that Preacher's deathtouch makes him a great blocker and making use of his high toughness often means not blocking smaller creatures so that he can avoid removal like Lightning Bolt and Shock
Common methods for indicating this include using markers or dice, or simply placing them in order on the battlefield
Not competitively, but I can see myself building a deck around Rubinia Soulsinger if I pull one in a dollar pack at my LGS
Halving Season's abilities won't change the number of tokens you create or counters you place, even if you're placing counters on permanents your opponents control
Miasmic Mummy: Limited, and a solid trick if you know you will benefit from discarding to your graveyard more than your opponent
Not to worry though, Manufactor is one of the most popular EDH cards from the set, just missing out on a top 10 spot at number 11 on EDHREC (going by raw number inclusion rather than percentage)