I completely fucked up the page for Google LoWaS; using the homestuck page counts instead of the all-mspa ones it's page 1685. Clicking on the (A) point brings up a dialogue bubble from terezi that includes "<-4LSO H1 TH1S 1S M3", making it clear her face is diagetic

Lord English explicitly does not exist in Universe A1, so I'm not sure how that would be possible.

I think that's misinterpreting it a bit; while Lord English cannot enter A1, he does have effects on it. the session glitch that means the A1 trolls weren't ectobiologized in their session and forced them to scratch is described by Doc Scratch and (I think) Aranea as being his calling card. Leaving aside that describing Lord English as not existing at any point in Homestuck is a fool's errand, he definitely exerted influence on the A1/Beforus session

I don't want to be rude, but a lot of questions in this are things that are explicitly explained in canon or things that could be worked out with a little thought, or even things that fall under the MST3K mantra (If you're wondering how he eats or breathes, or other science facts/Then repeat to yourself 'It's just a show,
I should really just relax) or, in more MSPA-appropriate terms: