Being in Reboot, I can't say for sure if the set is account transferable. Although Tera burning is VERY worthwhile for legion mules and link mules regardless.
I've actually seen this error, usually when my internet "hiccups" while i am loading up the launcher, Id just reboot the router and try again, or even just reconnect to your internet from the computer, usually fixes it.
First of all, what server are you on? Depending on that, there are a few different ways.
Reg servers: Bossing, droplet farming, and selling certain boss drops can be a good way to make money.
Reboot: Meso farming suicide Kanna at Bye Bye, Arcana Kanna
I can go more into detail as far as Reboot, but I am not as familiar with Reg server meso farming.