Question for the Duramax crowd

I just bought a 2025 1500 Custom Trail Boss with the 3.0. Im brand new to owning a diesel. I’m needing to fill up for the first time tomorrow and there are no “top tier” places around me as suggested by the manual.

Will I be fine filling up at a high traffic place like Sheetz / Speedway? Will I need to worry about additives if I use their fuel?

Side question, what truck cap do people own / recommend. I’ve got my eye on the RSI Sport EVO or a A.R.E. With similar side openings.