This is my understanding, and anyone can correct me if I am mistaken. For both GPA and GRE scores, neither of them on their own will get you into a program. There are many students with perfect GPAs and stellar GRE scores so instead they're used as more of a cut-off. Many programs have minimum cut-offs (e.g. requiring a minimum 3.0 undergrad GPA) and your application may not even get past the first round if those requirements aren't met.
To answer your question, your GRE scores are definitely important...especially for meeting those cut-offs. You should look at the average GREs of accepted students at programs and try to aim for those marks.
As for the MA before PhD, it's a complicated question/answer. I've heard that a lot of schools prefer taking students out of undergrad, whereas some prefer students with a MA. A MA is certainly not necessary to be admitted into a doctoral program. The most important thing if you do pursue a MA, is what you do within that time. If you lack a great deal of research experience, you could pursue a MA that has an experimental thesis requirement and really focus on your specific research interests. I strongly advise you "plan out" your MA program before enrolling. I went for the MA because I was in a similar situation in terms of a non-stellar GPA, and lacking research experience. When I applied to schools, I had a good idea of which professors I wanted to work with and I communicated with them when I started the program.
Publications...I'm not actually sure. I would certainly say for a lot of programs they are not a requirement, as I've known several people who've gotten in without publications. They will definitely help your chances and also look very impressive. From my understanding, it's also far from the norm for applications to have publications (especially out of undergrad). They're definitely something to strive for, but make sure you get posters and conference presentations on the way because those are great too.
From what it sounds like, a MA will be a good option for you. Best of luck!