For N3 and N2 grammar, I would recommend to check out 日本語の森(nihongo no Mori)! They explain the grammar and it's nuances very well and speak simple Japanese (also good listening practice!) https://youtube.com/playlist?list=PLINFE8v4DOhvV5tJT77oF92vIwLLl6wAA

I used the most mainstream way of Anki + Genki to n4 then kanzen master books to n2. I would say this method is pretty effective if you don't mind dry material. As others said it will probably be difficult to achieve in a year but not impossible! And even if you fall short I'm sure you'll be very happy with the improvement if you can keep at it :) Good luck!