Study resources that aren’t similar to LingoDeer and Duolingo?

I’d say start learning grammar as early as possible. I don’t see a reason to wait for level 10 since most resources provide you with vocabulary to use while learning the grammar.

Many people use textbooks but there are also many free resources online. There is a topic here for resources:

I did a lot of my early learning with Tae Kim’s guide and Cure Dolly’s videos (both of these can be found in the topic mentioned above.)