Diablo – Do the Orange Stars indicating a legendary drop appear on the quick (TAB) map

No, the way magic find works has no effect on items like the plans for staff of herding. Also taking off nephalem valor would not affect the outcome either.

The way magic find works is once the type of item that will drop is chosen it increases the chance that it will be a magic/rare/legendary/set item. But since the plans for staff of herding is most likely in its own category, it can not drop as anything other than it self and Magic Find will not effect its drop chance.

The difficulty you farm in does not matter towards your chance of getting them, it is just a question of how fast you can kill the boss or maybe get xp/usable loot while doing it.

From the diablo forums, the legendaries drop rate is not disclosed as of now.

Grimiku said: Increasing the difficulty will increase the amount of damage that monsters do, give them extra health, and reward you with more gold and experience. Torment difficulties I - VI, however, also give you an better chance to find a Legendary item, and that chance scales up with difficulty. Here's the breakdown for most of the difficulty changes that's in our game guide. Remember, monsters scale with your character, so you'll normally be fighting monsters your level, or the party leader's level in a multiplayer game.

Normal: +0% Health, +0% Damage, +0% Gold Find, +0% Experience

Hard: +200% Health, +130% Damage, +75% Gold Find, +75% Experience

Expert: +320% Health, +189% Damage, +100% Gold Find, +100% Experience

Master: +512% Health, +273% Damage, +200% Gold Find, +200% Experience

Torment I: +819% Health, +396% Damage, +300% Gold Find, +300% Experience

Torment II: +1311% Health, +575% Damage, +400% Gold Find, +400% Experience

Torment III: +2097% Health, +833% Damage, +550% Gold Find, +550% Experience

Torment IV: +3355% Health, +1208% Damage, +800% Gold Find, +800% Experience

Torment V: +5369% Health, +1752% Damage, +1150% Gold Find, +1150% Experience

Torment VI: +8590% Health, +2540% Damage, +1600% Gold Find, +1600% Experience

Reading the whole thread of the forums, the difference of drop rate seems low enough to not warrant that a fast run would get you less legendaries than a slower at a higher difficulties. If you make a run at Normal a lot faster than at Torment 1, stay at normal. You might wanna try Master or Expert since the differences shouldn't be drastic if you can run T1.

If it only takes you 10-15 more mins at T1, go with T1. Only with tries out will you know which setting will net you more legendaries. For my part, I'll be lowering to T1 since T2 is a tad too slow for my taste even if I got 4 legendaries in about 4-5hrs of play.