There is the option there for joyetech to cede validity and argue infringement, but the standard has been to challenge validity as the primary argument and infringement as an adjunct portion of the case.
For sure, the discovery process is going to be a back-and-forth issue - for both parties. Evolv is at a disadvantage somewhat in that regard, as you noted that most of the pertinent records are going to be in China.
I don't see jurisdiction being much of an issue: that's all spelled out in the first two pages of the filing. And according to a previous poster, joyetech has used the same court for filing suit so there is precedence of venue.
There's no such standard. Whether to focus on infringement or invalidity depends on the facts of the case, but Evolv first has to make a plausible argument of infringement. Otherwise, joyetech can file a motion for summary judgment on non-infringement and prevail. This pretty much puts the burden on Evolv regarding its infringement arguments right from the start. As for invalidity, that burden can largely be moved toward the end of discovery if desired. If you're client is a Fortune 500 company, things aren't done that way, but not every client is a Fortune 500 company.
As to jurisdiction, Evolv asserting that Joyetech China and Wismec has substantial, systemic, and continuous contacts with California in that judicial district isn't sufficient. Rather, there will likely be an extensive period of limited discovery and motion practice solely on the subject of jurisdiction. In view of the Supreme Court's J. McIntyre and Goodyear cases, it can be actually quite difficult to establish personal jurisdiction over foreign companies.