It's hard to answer that because we don't know your goals and tastes. Those are all dirt however, and each of them does some sub-low (at least) cut and things to the midrange/top end (especially if you rock those tone controls). I would start with after, just before the amp in this case just because of all that and because that's what you know. But then do try it out front as well (see below about that).
In either case keep that 50Hz all the way down - it won't give you anything useful to boost it or even leave neutral.
A side question. Should I put all my amp EQ settings at mid and EQ from there, or just go ahead and use the pedal straight away as each amp is already set? I noticed in the video Knight posted that his are all hovering around noonish. Personal taste, or suggested?
Again, hard to answer, but it isn't a bad idea to try that. Also note that not all amps have middle as flat; probably most actually. Guitar amps aren't designed to be reference like hifi; they are designed to impart a sound.
If you use multi amps then eventually what you want is to set the tone controls in such a way as to compensate or compliment what makes that amp different from the others - either you want something samey no matter what amp you're using, or you use different amps to get different tones.
As always, the godfather of EQ/distortion combinations. Six bands
before clipping and 6 bands after.
A banger for sure. I agree that EQ before (and after) clipping is very useful, but I also find that a single semi parametric (frequency adjustable from upper bass to upper mids) med-wide Q control does the trick there with less complexity (cheap graphics can have a lot of phase issues, noise, gain suck etc). That allows you to select the colour of your dirt/taylor it to the response of yer instrument by boosting a band before clipping, or remove mud or excessive crispyness by cutting. The one pedal I know of that has that is the Pearl (yes the drum maker, they launched a series of actually rather cool/unique guitar pedals in the 80s.... and nobody bought them because not a guitar company) OD-05. Smaller footprint is nice too. Still a bit of a sleeper, though people are starting to get curious.