I haven't tried Pelagos yet but considering that's where you unlock boats i would suggest having it earlier in progression than Gleba when wayward seas is installed

That also helps with giving access to modded content a bit earlier since as of right now the only "new" content you engage with in the first SEVERAL hours of gameplay is Muluna which is basically just space platforms++ anyway

I can't remember were it is, but can't you just fly passed all planets to get to pelagos?

By default, Pelagos is unlocked after Gleba's research tree, I don't think there's a need to change this behavior.

I don't think you need to change it too. Was it even you that made that requirement?

No, I'm not the author of Pelagos mod :)