Magnoliee:
a big cast. And I tell myself it's good for my brain cells
I like big ensemble casts (not only BLs) if the story and execution is really good, but yes, it's a challenge for the brain cells.
In the case of GMMTV (e.g. "P10L", "We Are" ...), it helps me quite a lot that I know the actors, so I can at least recognise them individually and mentally sort them out in my mind by actor name rather than character name. Otherwise, I would have to watch the first episode (or first part of movie) a few times until I know the characters. I remember the first time I watched the excellent movie "Gosford Park" (non-BL) how totally lost I was by the many characters in the top-notch ensemble cast, but after a few re-watches I finally got to know them all. Of course, that's a two-hour movie - re-watching 24 one-hour episodes of "P10L" would be a pretty major additional time commitment!
The easy-to-remember Anglicised Thai nicknames are also a big help here - if these were Korean or Chinese actor names, my "system" wouldn't be much of a help!