I will reiterate what the others said, mixing same with same is best.
EXCEPT for PearlEx, like Elsa said. I throw that into everything else like no tomorrow. A little silver sparkle here, some gold shine there, Let's make that black ink look like it's got stars in it.
Typically if I add PearlEx to anything that already binds well with paper I don't need to add any gum arabic to it. BUT I will usually do a test first, and make sure it flows well. If I have any trouble with flow or with the sparkles staying down, then I'll add a smidge of gum arabic, but not as much as you would when making a purely pearlEx ink. From my experience.