PhD Student, written my first paper. What are my next steps?
First of all, your advisor should judge whether your paper is worth publishing. If the answer is "yes", then go for it and follow the process outlined in the author's guide of the respective journal/conference/etc... 

I don't know about the habits in finance, but a 70 pages paper sounds rather long. Maybe you should condense it (if possible / appropriate) before you ask your advisor. But it depends on the habits of your field (which you can learn by reading publications of others).

If your advisor has no answer for this question, go look for another position/advisor. 

If they liked your work and ask for new ideas, you are on a good track - write down some proposals and ask for a discussion about the ideas.