Yes, what you want to do is safe to do online.
If those are the only things you intend to do, I have a few recommendations:
If you are having your personal OLED modded by someone else, please ask that they install no NSPs, Tinfoil, XCIs, and no emunand, as all are potential ban risks and you don't need any of them. Ask for the bare minimum required, ie Hekate and Atmosphere.
If you are buying a "premodded one", obtain proof that it has access to the eshop and online services and is not already banned. When it arrives, boot it into stock and before connecting it online, perform a full factory reset, and completely reformat the SD card to FAT32, as most sellers tend to load the console with a ton of bloat like "lots of free (pirated) games" which can get you banned, and bundled software you don't want or need.
If you have to do the latter, you will want to install custom firmware on your own at that point, from scratch. If the process is generally the same as installing custom firmware for non-hard modded consoles, you can follow this guide:
https://nh-server.github.io/switch-guide/user_guide/sysnand/sd_preparation/