Been trying this method recently and generally happy with the results. That being said, I can't help but feel I'm still making a few mistakes:
Steak lets out quite a lot of juice when slicing it, even after it's been rested for 7-10 minutes. How do steakhouses serve a steak on a plate that almost doesn't let out a drop when cutting it?
Cast iron, smoking hot - is there such a thing as too hot? I use avocado oil with a high smoking point but the oil always seems to burn rather quickly, even in just a few minutes of searing. It turns into this ugly brown color and doesn't let off a great smell either.
Steak is unevenly cooked (i.e. top vs. bottom). Should I be flipping it while in the oven?
The method on the link talks about how it is more consistent, but really it has as much potential for going wrong as any other. That doesn't mean it's not a good method, just that there are some gotchas. To answer your questions:
Good steaks are juicy, there's nothing bad about having juice come out when you cut it! If juice doesn't come out when you cut it then it's probably too dry
With this method you can't get too hot, the idea is a quick sear at the end of the bake. However, you have to get the temperature right when it comes out of the oven or you must cook it for longer than a quick sear to get it up to temperature. The right temperature depends on the thickness of steak, a thin steak cooks much faster than a thin one, so you pull it from the oven at a lower temperature or the heat from the pan frying will overcook it. The method on the article says for medium to take it out of the oven at 105°F and then sear it to 130°F. That means your sear is supposed to add 25°F. This may work with a thinner steak but a thick one it means a lot more time searing. I'd bake a really thick steak up to 120°F before searing it to get to medium
There may be a difference in heating between the conduction of the air on the top and the metal on the bottom which is causing uneven cooking, it all depends on your oven and the pans you use. I'd be tempted to try a baking tray rather than a cast iron pan in the oven as it should be more even, but flipping it is a good idea as well and may be all you need
So, a couple of tweaks should get you there. One thing more, with a thick steak I'd let it rest for 10 minutes rather than 5, don't forget to cover it to keep it warm.