1) V1 (Erista), V2 (Mariko).
Mariko + Switch Lite are V2 - to tell if you have a V2 Switch they had the newer Nintendo Switch boxes which were all red. They make the statement of better battery life. They released Aug 2019. You'll have a model number of "HAC-001(-01)", Those are the V2's.
With a V1 they had the unpatched (original Switch), and then the patched (Nintendo fixed the exploit of the RCM bug with the Nvidia chip). You can find out those on various websites discussing what the model number parameters are of having a hackable Switch are, even on GBATemp.
2) If you have a V2 Switch, then even with the modchip, you currently are not able to install Atmosphere.
If you have a V1 Patched with chip, then you can.
3)There's numerous guides how to install Atmosphere (on unpatched Switches) and then the original one on here from Masbass is actually pretty good because it's discussing doing it with the SXCore chip. It's going to be a mix between looking at a guide like NeverCholt has on Youtube for Atmosphere and then figuring out how to make it work with the SXCore.
So basically; just look at NeverCholt's Youtube (he also has a website too with step by step instructions from the sd card to installing Hekate/Atmosphere, do a quick google search) on how to format the SD Card / install Atmosphere and then use what Masbass put in the original post to help you because you'll be doing it with the SXCore chip..
4)if you use Hekate / Atmosphere, then Hekate will partition the SD Card within it. The instructions on Nevercholt's webpage explain how to do it via Hekate.