How many lessons/reviews a day should I do?

Learning all kanji using only WK in one year is ambitious, it depends a bit on your prior knowledge, and your willingness to review kanji outside of the usual WK schedule. If you can focus on kanji every day and if you are committed, WK may even slow you down. However, taking your time is important for long-term memorization, so going (relatively) slow as WK enforces is actually a good idea.

I recommend the self-learning userscript to “pre-learn” the content of later levels to reduce delays from new content. You can use it to preview and drill higher kanji more conveniently. It is also good to refresh a few prior levels.