I have a new venture still in the works as well. As far as pre-launch marketing goes I would just start by mostly researching. Research who you're going to advertise with and set everything up so that when your site launches your not trying to come up with marketing ideas. Develop a marketing calendar of what you want to accomplish and see how to use your budget to effectively accomplish that.
Planning ahead always benefits the marketing process than hitting the panic button at the last second and spilling a ton of cash into a channel with no ROI.
If your marketing is going to be strictly digital then read up on SEO and other digital marketing techniques.
Nothing compliments a low cost digital presence like face to face social marketing.
