Link skills to choose from?

Well, yeah, but my hands would be probably full with training, especially when the time frame given is only 2 weeks between new classes released in MSEA. (Except for Lumi/Kaiser and Xenon, estimate around 3 weeks) So yeah.
Like you said, we're gonna get the character slots anyway.
But the question here is about priority, i.e. Which link skill should get first.

But in terms of training to level 120 first none of them are important except for Mercedes, and if you're maining Xenon all of them are important except for Kaiser. Also, you can pretty much finish it in two days with the know-how, you just need to make sure you get to 70 at least on the first day and then you're set for the second assuming you're free on both of those days since a Xenon should be able to demolish Evo world.