Hi Shakezilla,
So, my experience (including both personal and from what I've read here) is: If everything you do is "normal" within their process (for example, no messages to them from your Inbox), that USCIC will meet their timelines or come very close to them. (But, I had to correct a passport number, and I strictly followed their instructions on how to send a message requesting to correct a passport number... and they ignored it for 5 weeks.)
Now, to answer your questions:
Q1. I'd recommend giving them at least a few more days. Since this sounds "routine" and within the norm. Let the weekend pass and let it get into the middle of next week.
Q2. Waiting for the 2nd email (to the beneficiary) is (practically speaking) the only option. I don't know whether they (as foreigners) are able to create an account. But to be linked with you as the beneficiary, their account will have to be created on the email you listed within your sponsor's half of the I-134. I suspect a different email address won't work (i.e., to make that linkage to your sponsorship application). And if they jump the gun to create the account within that listed email address, but without waiting for the USCIS email, it *might* just gum up the works.
If for whatever reason, you eventually call them, the tier one person that you'll eventually get (and I got one within 10-15 minutes - not so bad, as these things go), will likely simply give you the standard answer ("wait, be patient, it's within permissible timelines, give it time....") But if/when you eventually get further concerned, then ask to speak to a Tier 2 officer based on urgency. That will get you a promise to expect a callback from the USCIS Tier 2 within 72 hours (working hours, I certainly presume, within 7 - 7?) And that timeline also doesn't always seem to be met. (But be sure to carry your phone everywhere. And program your phone to receive USCIS numbers as a known "contact", or you'll likely experience the infamous "they ring once and then it drops". I've known those USCIS numbers to program, to be 202-838-2104 and 202-838-2200)