could someone link me to a guide
There isn't always going to be a "guide" for things like this. Sometimes you're just going to have to Google things for yourself and figure them out. If you can't figure things out, then you can make a post that carefully explains the particular questions you have.
Checkpoint runs on your 3DS and decrypts your save data; you can then copy it off your SD card and use it elsewhere. To copy things off your SD card, you can use 3DSync or FTP. microSD Management is another option on New 3DS units, but it uses a very insecure protocol and us usually not recommended. Or you can just insert your SD card in an SD card reader on your PC, but things tend to go wrong if you repeatedly move your SD card around.
Checkpoint requires CFW to be installed. JKSM is an alternative that can be run through "userland" exploits that are not persistent, but almost no one does that anymore.
Mii Plaza is a major stumbling block. No one that I know of has come up with a good solution for fully saving and restoring Mii Plaza data. (I would love to learn the alternative.)
If you have SD card data that you haven't backed up with Checkpoint, it can still be manually decrypted on a PC using ninfs or threeSD. (ThreeSD is considerably more user-friendly, though it is still much easier to use Checkpoint if your 3DS is still fully operational.) Both of these options will require movable.sed, your 3DS encryption key, which is usually generated when you install CFW or can be extracted from a NAND backup.
Pokemon Bank is tied to your NNID. NNIDs can only be moved to a new unit by System Transfer or by calling Nintendo technical support. If you have installed CFW, you can also use PKSM as a completely offline alternative to Pokemon Bank.