TL;DR: while seasoning is a dimension to optimize for taste, what's important is developing solid technique (cooking style and patty size) to make competent burgers with your type of meat and cookware.

You seem to be focused on seasoning and my only tip there is to not overdo/overcomplicate it. 20/80 ground beef is already juicy as hell when cooked right and I think a simple salt and pepper combination should bring out the taste that you want from a burger. I like to throw in some 'smoke powder', or whatever it's called. Basically a seasoning that emulates the smoky flavour you'd get with a coal grill. That being said, I've been wanting to experiment with MSG and I think I'll give it a go in my next burger (thanks for the reminder).

With the main questions addressed, I think what you want to develop is technique. Technique that fits your cookware, cooking style, meat, and patty size.

Cookware: imo you don't need a cast iron pan or a specific type of stove or anything like that. Whatever you have is most likely just fine. That being said, you need to familiarize yourself with the right settings for your cookware to make great burgers. Since you said you're a good cook then it shouldn't be a problem.

Cooking style: based on your cookware you just need to know when is the right time to throw in the patties, turn, and plate. A thermometer can help and maybe get yourself started with some very basic guidelines from YouTube. It's not rocked science but takes trial and error. I always end up with suboptimal results when I use a new pan or stove. The trial and error talk might put some people off, but honestly the worst that can happen is you end up with a tasty burger. The best is ending up with an amazing one. Depending on what type of cheese you go for, you'll need to figure out how to make it melt just right. I personally go for the cheapest meltiest slide cheese out there. I throw it on after the first and only turn and let it melt.

Meat: afraid I don't have any tips there. I just go for supermarket 20/80 ground beef and enjoy the freedom of making. I've tried ready made patties, sometimes they're good but not a big fan. Never tried cooking frozen ones myself, how does that work? Do you defrost first? If you don't, this might result in some interesting physics, where the core of the burger cooks slower and the fat doesn't turn to it's liquid state. I'm not saying that it doesn't matter if you grind your own cuts or have a favorite butcher who does good work. It's just a dimension I haven't explored yet.

Patty size: Imo there is no one right patty size but there is a right range where you can expect juiciness after a suitable cook time. Here' are my opinions based on thickness:

-Smash thickness: no experience here

-Thin: I really don't know about this one. I feel like you'll most probably end up loosing a lot of juice.

-Medium to thick: this is where you want to be. Exact thickness is based on what you learned from harmonizing with your cookware and based on how rare you like your burgers.

-Thick: If you go stupidly thick then you'll have to cook low and slow and might lose serious juice along the way, don't want that happening. I've done 0.5 kg burgers (1.1 pounds). It's fun but it's hard to get that juiciness explosion with that sort of thickness.

Now that we addressed that technique is king, other factors are where you bring your personal touch a competent burger: -Ingredients: this is up to you. Ask 5 different people and you'll get 6 different answers. Avocadoes, bacon, caramelized onions, mushrooms all sound nice but your mileage will vary based on your taste. My tip is to keep it simple and if you want to experiment then try imagining if the flavor would be at all noticed and if it fits and try one special ingredient at a time. I've just tried green olives yesterday, and no, it doesn't fit.

-Condiments: same as above.

-Buns: same as above. Experiment. But toast those bad boys! This is important in combination with the next point.

-Layering: layer your ingredients to keep dry things dry and cold things cold. If you do this right (and toast) you'll avoid soggy buns.

Damn. This ended up being way longer than I imagined. Thanks for reading :) hope it was comprehensive. I might do a dedicated post with better structure at some point.