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That "wasted" steam in the dead pipe will help heat your basement if you want.

I have always put the air vents in the boiler room when possible.

The idea is to have all working/moving parts in one place and hopefully near a floor drain.

It will absolutely delay the emitters getting steam (steam can't heat both at the same time and rate as one) but that's all I'll say about it hopefully

Well….except that steam will get used to heat that "dead" part of the main, and steam will have to fill it. Therefore I think you should count it. Or even better, put your main venting before that dead part of the main.

Fighting anecdote with anecdote, here in North Jersey it's 95F at 2pm and the voltage in my outlets is 121.9

The grid is fine, updated, and constantly being improved.

Induction motors with conventional controls will not shut down with an 8% voltage drop. They will draw more current and run hotter. Depending on the load and service factor they may trip out an overload and shut down after a while. It may shorten their life but 8% isn't going to make them shut down in most cases.