Are you remembering the readings and meanings in spite of not remembering the mnemonics?
if you are, then I would only skim the mnemonics for now, and only worry about remembering or making your own, when you’re having trouble remembering the meanings or readings of the vocab or kanji. When you’re a bit further along in WK (10s or 20s maybe), you could use the [Userscript] Keisei 形声 Semantic-Phonetic Composition script. It can help you lay connections between kanji with common components, which indicate a common reading.