You should start learning grammar right away, as you can’t do much in the language without it. Either literally right away or if you prefer to know some kanji first maybe by level 5. Waiting longer would be a waste in my opinion.
For dictionaries, jisho.org is fine. Pretty much all J–>E dictionaries are based on the same information anyway. When you do start using Japanese only dictionaries, I personally prefer https://dictionary.goo.ne.jp.
As for when to start reading, it largely depends on how willing you are to go slowly and look things up. I started reading somewhere around level 30 if I remember correctly. The first few manga and certainly the first book were quite challenging, but that will be the case no matter what. Plenty of people start reading much earlier than I did.
Whenever you do want to try reading something, it helps to read with others so you can ask for help when you need it. There are many book clubs hosted here on the forums, including some targeting beginner and absolute beginner readers. The expectation is still that you’ve learned at least basic grammar, but once you have learned N5 grammar (and maybe some of N4) you can start reading manga with the groups. There will still be a lot you don’t understand, but that’s why we read together to begin with. You can of course try reading with the groups before you have that basic grammar knowledge, but I’m not sure it would be worthwhile.