The idea of an antiemetic, such as meto, is that it helps to reduce the chance of vomiting, statistically. It also helps to increase the absorption of sn as well(I don't know the scientific terms, only the basics. It has to do with gastric emptying, as for helping overall absorption). Some people vomit even if they follow Stan's guide to the letter. Others succeed without anything but SN. All we can say is that your chances are higher with meto.
I will say that volatilepotato did it without meto and I haven't heard back from him since late April. We chatted a bit that night. He literally had no antiemetic whatsoever and still appears to have succeeded.
Everyone's body is different. If you want your best chances, meto is worth obtaining.
Yes, having multiple cups of sn is a good idea. If you vomit the first, having 2 extra cups is generally a good idea. Only drink the others if you vomit though.
Edit: I did forget to mention that I've heard time and time again that most people who succeed with antiemetics still vomit. But like I said, although it decreases the overall chance of vomiting, what appears to really be important is that it DELAYS you vomiting, and helps gastric emptying. I forgot to clarify that part.