Stationery is very competitive field where folks who do well are usually those who are able to distinguish their product with a high degree of personalization. The forum for your business that will cost you the least to set up and probably have the most significant return will the web. A well put together website promoting your art work and unique designs is a must. At the outset you may want to have e-commerce on your site or to save money, you may want to start out with just a display and showcase of your work with orders placed over the phone.
Other things to research are incorporations, contact business associations for your industry, business loans and financing and a well though out business plan. Take advantage of this excellent forum and our website that gives you tons of free information..
Designing your own stuff is great as you will have unique products. But that will mean sourcing all kinds of raw material and then printing it and marketing your stationary.
It would not be a bad idea to source products from a vendor or a OEM. That way you can cut costs upfront.
Check out Etsy.com. Stationery businesses do well on this site. At this time it's been three years, but this may still help.
The basics in starting a business is to look for the competition in the market that your product is going to face so that you find some innovative way to make it look the best choice for the customers looking for it. More importantly when consulting an agency with your idea you must have a background check on how this agency deals with clients. Apart from that all things can go smooth and easy if you find a reliable partner who has knowledge about stuff that you are new to.