It helped a lot but I will have to review certain sections a few more times to truly understand them. Should I keep going with it or should I use another resource? When I got to casual patterns and slang I was pretty much completely lost and don't think I'm anywhere ready for that. Special Expressions and Advanced Topics might be way too hard for me.

Should I use Genki and/or Japanese the Manga Way to go over the same material but with a different teaching method or is it a waste of time?

It could be worth skimming through them and just making sure you understand what they teach, but I wouldn't spend long on re-hashing old material before moving on.

It's my firm opinion that unless you're specifically studying for a specific test grammar should be studied on an as-needed basis. Know all the words in a sentence but have no idea what it means? Yeah, look that grammar up, get yourself some examples. Otherwise don't even worry about grammar.

You can do a hell of a lot more with vocabulary than you can with grammar.

Well right now I'm doing core2k/6k and am also doing a Tae Kim grammar deck. Since I'm gonna have more time now that I'm not learning new things on Tae Kim's site, I was wondering what I should do with that time.

I've tried reading native materials and websites but my vocabulary is too low so I'm not sure if that's the best thing to do.

Work on your vocab. There's a lot of ways to go about that. Core is probably the most common around these parts, and it's what I use as well.

"but my vocabulary is too low"

Then I think you know what to keep working on!!

I agree, do the vocab and when you encounter grammar points you don't get, look them up.