I think this guide is quite good – A Year to Learn Japanese. There are also other guides.
IMO, you can learn grammar immediately if you don’t have problem remembering basic vocab in the grammar book.
Vocab is a different thing, grammar exercises might not give enough of that. Kanji could be a good way to learn and retain a lot of words (despite unexpected word meanings away from the Kanji sometimes).
There is this big resource Wiki from Japanese Language > Resources
PDF and the linked thread could give some good strategic advice for language learning.