There is no rule on % to spend, it is not about the size of your budget anymore.  Today you can have tremendous impact through social media, influencer marketing, SEO, SEM,, etc.  It is about being relevant and timely with the right message to your audience.  Find your key messages and be consistent in communicating them across all channels for the best results.  Track andmeasure everything so you can test and learn as you go.  As you get traction then you can start to invest further to grow.   Be scrappy and resourceful whether your budget is small or large.  Find the tools that work best for you.  Good luck!