I always weigh out 5 oz. of ground beef and form it into a rough ball. When I have all the balls ready, I start squashing and forming into patties. All the pros say to be gentle and work the meat as little as possible but whenever I try that the patties fall apart. When I get the ball squashed to a rough circle I start pushing in from the outside, holding a couple fingers from the other hand in the middle of the patty. Going all the way around this gives me a fairly firm edge that doesn't fall apart and I also get the indentation in the center. I never have a problem with them turning into little meat loafs on the grill. When I'm going all out I grind my own chuck roast in the food processor, but most of the time I use the Costco 88/12. I also tend to put on a fair bit of seasoning, usually McCormick's Montreal Steak Seasoning or, as second choice, Weber's Chicago Steak. Aside from that I go where the mood strikes me on seasoning. Sometimes a bit of Worcestershire, sometimes a bit of ground chipotle.
As for cooking, I go by time and appearance. I try for a very hot fire and do 3 to 3-1/2 minutes on the first side, then a minute less on the second side. Lately I've been grating together yellow medium and white extra sharp cheddar, piling it on top about a minute after the flip. The medium cheddar melts nice and the extra sharp gives a nice kick. I always leave the cover on unless actively doing something on the grill and this tends to eliminate flare-ups. Of course, the 88/12 doesn't have a whole lot of fat to flare up.
As for the Thermapen, check out the ThermoWorks web site. In addition to the Thermapen they have a number of much cheaper models that are reliable and just a bit slower than the Thermapen. I've found that for $80 in savings I can live with a temp reading taking 3 seconds longer. They have a couple nice models on sale right now for $19. I strongly recommend going right to their web site and not to a third party. Some unscrupulous merchants are charging way more than the company does on their own web site.