The first one has rough guidelines for some verb endings, as you correctly observed. There are some pairs that are even a rule. I don’t think it adds much value to learn these rules, though. Can be interesting to read up on, but I wouldn’t necessarily learn them.
A good resource for these transitive/intransitive pairs is A dictionary of basic Japanese grammar (DOBJ) page 585ff.
For the second one, it’s called Keisei composition, and you can find support for Wanikani in this thread: [Userscript] Keisei 形声 Semantic-Phonetic Composition
It doesn’t work with every Kanji, but it can be helpful.
I can’t think about any other tips that might be helpful currently. I found that after you expose yourself long enough to the language, you will pick up on that stuff even if you haven’t “learned” it. And generally it sticks way better that way, instead of having to memorize a rule.
There was this thread recently about godan/ichidan verbs. And sure you can learn wich ending is which and go to your conjugation tables and build sentences at a glacial pace, or you can just expose yourself to the language until it all starts to feel natural ^^. It’s the same for these tips in my mind.