The question on downloads is a huge roadblock in light novel fandom, and everyone tackles it differently. I totally get wanting EPUB or MOBI files, that's my jam too for offline reading on my Kindle or phone. The sheer convenience of having your whole collection, especially for long-running series like 'That Time I Got Reincarnated as a Slime', formatted perfectly is unbeatable.
But I'm not sure I can give the kind of straightforward download links people often look for. The primary hurdle is that for most modern and popular light novels, official digital releases are locked behind purchase or subscription on platforms like Amazon Kindle, Kobo, BookWalker, or J-Novel Club. These storefronts use DRM, so the files you get aren't simple EPUBs you can transfer freely. There are tools and discussions about DRM removal in certain corners of the internet, but that's a legal and ethical gray area that makes me uneasy to promote.
A more reliable path I use for non-DRM files is checking if the publisher offers them directly. For instance, J-Novel Club members can download DRM-free EPUBs for every volume in their subscription. It's a paid service, but you're directly supporting the translators and publishers, which feels right. For older or completed series, sometimes fan translations that were done before official licensing are still floating around as EPUB packs on aggregation sites, but their quality varies wildly and the legality is, of course, dubious. My advice usually bends toward patience and saving up for the official digital copy – the translation is consistent, the typesetting is professional, and you're voting with your wallet for more series to get licensed.