You wrote you love to do marketing, and I think that's ok. Given tour profile, I think both Quantitative Marketing and Marketing Strategy would work for you.
I'm in Quantitative Marketing, and my background is in Finance. The new student we have here has a background in Accounting. That kind of background can be useful, specially if you study things like customer lifetime value (which is like valuation methods applied to consumers, with discounted cash flow). Also, we often study the impact of marketing on outcomes like shareholder value. I don't think you would be considered nontraditional here.
When are you going to apply? If you are going to apply soon, then there is something that looks more like a priority than any of the things that you listed: decide the discipline to apply (e.g., Marketing), your topics of interest, and find the right schools to apply (this can take a lot of time, and is really important).
1 and 2 - Papers are good. If you can finish them and submit in time, I think you should do it.
3 - I'm not sure I understand what you meant by "senior" here. For me, a senior wouldn't be a tenured professor or someone like that. And, in that case, not someone who can provide a strong letter. So, I'm confused when you say you have a strong letter from a senior.
4 - An SOP that is used "to explain my experience, non-traditional background, and my poor grades" wouldn't be an impressive one, in my opinion. You would probably talk too much about things they don't really care that much, and too little about the important stuff. This is a Statement of Purpose, not an explanation of what you did in the past. You can bring your background if that can help you to explain your purpose, but should not waste much time explaining things from the past.
And, since you don't even know if you're going to apply to marketing, innovation, or something else, you don't have some critical stuff for your SoP. For example, what are your research interests and what is your purpose in studying them? Or why do you think that the specific school you are applying to would be great for your research interests and purposes?
5 - Your GRE is not bad, but certainly it doesn't look impressive. It's acceptable, not strong. At least for good schools, they should get several applicants with a score that is better than that. I wouldn't be happy with that score, if I were the one applying.