i'm a huge fan of costco's meat department. they've done well for me for many years. i try to buy cryovac when i can so i get better value and cut my own steaks and freeze what's for the next cook(s).
there are many different burger blends you can make. i'd recco you start simple and easy; ground chuck roast. around $4.49 a pound, or more these days, you're getting a nice 75/25 to 80/20 burger, depending how much fat you seek when you buy the chuck roast. i tend to buy a 3.5 to 4 pounder which we make our burger from.
the burgers in this cook were 4.5 ounces each. 5 oz is a nice sized burger. 6 oz is a huge burger. 8 oz is if you're a glutton for a hefty burger. IMO, 8 oz is insane, you might as well cook a steak!
when trimming a chuck roast, cut off and discard the silver skin. silver skin does not grind.
i'll have to check my grinder to advise which plate i'm using but i believe it's the largest grinding plate and i always do a double grind. semi frozen meat is best so the fat won't gum up in your grinder. yup, you'll be working with cold, near frozen beef but it works well to grind like this.
my KA is a 325 or 350 watt one, heavy duty, whatever that means these days. i run on speed 4 when grinding.
you can mix is sirloin meat with chuck which these were which make for a nice steak burger. very beefy in flavor without being too dry or mealy where your burger will fall apart. so the trick is enough fat, but never too much fat.
i've done some 65/35 burger on my gasser and those burger generated some serious flame kisses.
i've done 100% ribeye burgers, for fun, and those were great!
my fave would have to be a 50/25/25 of chuck, short rib and brisket, in that order. to me this is the best beef burger flavor and fat wise. many higher end restaurants, ($18+ for a burger) will run this blend and charge you for it.
reply back with any other questions you might have. fresh ground beef is so much better than store ground mystery burgers.
you can grill, flat top or cast iron your burgers. all work well and all have their place, depending what you want to eat.
but the spread. you must have a good spread for your burger. and so much more to go with it for that next-level experience.
welcome to the grind your own rabbit hole. there's a few people here already. they know who they are.