ichi.moe works pretty well for me, especially when I’m not sure how the words are separated. It’s nice that it breaks down conjugations and gives different possibilities. One thing to be aware of: If it isn’t able to parse a part of a sentence, a lot of times there’s some casual contraction it doesn’t understand (things like の → ん). Even if you don’t use ichi.moe, it’s worth a look at this Quick Contraction Reference
I use Jisho as my main dictionary. There are lots of other good options but I like the interface. You can look up kanji with it too, not that you’ll need to do that much in this book club.
For grammar, I usually use two different books (I find paper easier to look up grammar on for some reason, but I should probably get better myself at looking things up on the internet). If it looks like a particle the first thing I go to is “A Dictionary of Japanese Particles”. If it doesn’t appear there, or if it’s not a particle, I go to “A Dictionary of Basic Japanese Grammar” (I only have the basic volume but there’s also an intermediate and advanced). With that said, I’ll still use Google a fair amount, similar to how Jiell does.
I haven’t found a great all-in-one resource for helper verbs. Over time I’ve gathered a bunch of info from different sources in my personal notes. A good place to start is the Tofugu article on Verb Conjugation Groups. At the bottom there is a list of “Related Grammar” that links to articles on common helper verbs.
If you like looking up sound effects, try The Jaded Network SFX Search. I skip looking up that kind of thing a lot, but it can be fun.
I admit I use deepL sometimes. Others have really cautioned against it because it can be completely wrong (where was that super recent discussion about this?). It doesn’t have much context about the story, and sometimes it’ll interpret a word’s meaning completely incorrectly. When I do use it, I’ll just take it as a hint, and go back to ichi.moe or Jisho to understand exactly what’s going on so I can work through the sentence on my own …or I’ll decide the AI translation doesn’t make sense at all.
If you haven’t seen The Ultimate Additional Japanese Resources List!, there’s a lot of good stuff there.
And of course, as others have said, asking the book club is a good option. People love answering questions here (thanks everyone!). A lot of times your question has already been asked, or somebody has posted their translation of the sentence.