So I've never done these on my cars and I don't know if its ever been done on my c43. 56K miles.... I think it's a good time to start. I've read that these two are what we want to put in our cars.
Gasoline System Cleaner - ~ Once a year
DI Jectron - ~once every 1200 miles (I think)

Question I have... What one should I do first and why? Does it even matter?

I have not used these products... It seems the GDI chemistry targets the pistons crown to minimize LSPI.
Hopefully it does not hurt the tank components.

At least it won't clean the intake valve carbon deposits.

does not matter. Just carefully read the instructions to see if you were supposed to change the crankcase oil after a certain amount of uses of these products. You don’t want to dilute your oil. In the future, when looking for gasoline additives just find the product with the highest amount of PEA, which is generally the red line product.

I throw in the DI Jectron maybe once a year just as PM for the injectors.
I dont see it hurting, but at $20/can its not something im doing monthly either.
Also as mentioned, read the can. I believe it doenst play well with ethanol, so i will run a tank of just 93 before using since normally i run E20.

I always run 93 so I think I should be ok here. Yea, I'm also not looking to run this multiple times. Just thought I'd run it once for piece of mind.
I started with the DI Jectron w/ 93. I'll probably run a clean tank before I throw in the system cleaner.

I typically use the 20oz bottles of Chevron Techron fuel system cleaner, and the Berryman's direct injection intake cleaner before every oil change.

I tried the Liquimoly cleaners a couple of years ago, didn't see anything wrong per se, but they were pretty expensive for what you get