Seriously? Customizing a WordPress Theme costs between $1,000 and $2,500. Building (Design+Front End Programming+Back End Programming) a fully-fledged WordPress magazine theme can cost between $15,000 and $20,000.
If you are not a software developer, and your start-up core product is software: just don't do it. Don't take OP advice. This might work out if your product is physical and you are using the web to deliver. (Also there are cloud services that will help you and are cheap).
Anything that involve software requires co-founders to be technical. Web Development is as expensive as hell. Small features requires lots of time and Freelancers bill hourly. I'm telling that because I just finished some custom slider for a client costing him more than $1k. Yes, just an image slider.