I don't have specifics on maximum dosages. Maybe talk to your pharmacist or doctor about that.
I choose an area for my electrocutioner to work on and cover the whole area. So, for example, I might do one entire cheek, or one side of the neck, or the jaw and front of the neck. There is no point in covering more than that, since she can only do so much in an hour. I cover it thickly, since I am quite sensitive to pain. My electrologist has to scrape me off the ceiling at times!

I have had no trouble with that kind of quantity. Note that the principle risk is of irregular heartbeats. I get those anyway from time to time, but I have had no increase in them as a result of using Emla.
Some tips for using Emla... Apply it at least one hour before your appointment. Immediately cover it with plastic wrap (e.g. Saran Wrap) and tape down the edges to make it airtight. Keep the cover on until the last second. I let my electrologist remove it when she is ready to start.
Yes, wearing plastic on your face is embarassing, but it's what is required for adequate pain control.
For additional pain protection, cover the plastic with a layer of gauze, and then tape a second layer of plastic wrap over that. While this is more obvious than the plastic alone, it looks like a medical dressing for some injury, and is less likely to raise comments. And the extra insulation helps the Emla be absorbed by the skin.