If I were in your position I would try and get through the Genki 2 path as quick as possible and then, if you have time, add grammar points from past paper questions where you failed the question due to an unknown bit of grammar. Or do a mix of both at the same time. Actually, probably a mix of both at the same time. People say Genki 2 takes you to the point where you can pass the N4 (I never took it so I have no idea) so that should be at least a solid foundation. I think patching over the cracks in your knowledge based on prep materials is likely the best way to go.
It might also be worth reading all of the N4 materials on Bunpro even if you aren’t adding all of them before the test. You can read, say, 10 points then use the cram mode to drill them for 30 minutes or something if you really wanna go the extra mile.
I can’t give you a ranking of important points based on the JLPT as I have never had much interest in it but in terms of real life usage I would say the following (although they are all eventually important):
- All the different forms for conditionals
- All the different ways of reporting something or simile (そう・みたい etc)
- “Transitive” and “intransitive” verbs
- “Potential form”
- Actually understanding particles