Hmm, I will share my suggestions but know that I'm no millionaire yet so just take what is good, assimilate the relevant, and leave out the rest
1. Create a platform for other designers to join in your idea of creating unique and beautiful wallpaper designs. The obvious choice is to create a website that specializes in that, think Etsy but for custom wallpaper designs. This way you get others to help out, and you help others too. And in the long-term you would want it to free you to take on other endeavors in life, not 'shackle' you down as the main designer.
2. IMHO, I believe that by working in that industry first to be the best way. You are doing so blindly, but with the purpose of observing how others run a business from the inside. This alone is priceless, while at the same time you get income coming in too. Think of it as learning the ropes while challenged by real-world assignments + getting paid
3. You can also use your spare time to begin producing a few designs and begin marketing it to places (like the furniture galleries you mentioned) that sell wallpaper, just so to gauge their interest in your products. This will give you an idea how the industry you are trying to service really works. Plus, you get to build rapport by first offering value instead of looking to take.
Just my 2 cents. Hope there is something useful in these paragraphs. Cheerios!