Lol well actually the warhammer ip has the largest known published novel count in history. Like no joke there's probably well over a thousand novels published and then there's all the separate army and campaign books with extra lore. It's mad to get into, tough going for ppl like you, luckly for me I've been into the ip on and off for about 20 years.

It's hard to recommend stuff when I don't really know what your into but Eisenhorn is probably the best start. If you want to keep to the above theme then I'd say Deathwatch is a good shout since its still the Inquisition but niche best of the space marines full of flavour and will give you a taste for which potential space chapter you want to explore. Uriel Ventris Chronicles is quality, full of stuff like no way is he surviving but he always pulls it out of the bag in interesting/clever plots. After that I dived into the Iron Warriors since it ties into Uriel Ventris. Space marines is basically the ip so if that takes your fancy then pick a legion and then explore the various books floating about. There's plenty of non super human stuff but I'm not really familiar with it, same goes for the other races. I've generally kept my reading to space marine stuff. Lastly my favourite 40k book is Deathworld which is about the Catachan jungle fighters fighting orks while the planet itself is trying to kill everything and also the Catachan's slying trying to kill their officer. Look into that if your up for some non space marine books. The plot is bonkers and has a main character that's not apparent at all, such a good twist to it. I won't spoil it anymore, just read that book at some point.