Hi GD-OT, I majored in Graphic Design as my undergraduate major and found myself in a similar situation. As of right now, I have just been accepted into an OT program starting 2014. I decided to take my prereqs at a community college and then applied straight to OT school as opposed to becoming an OTA first. I didn't even really look into becoming a OTA, so I really can't speak to that path. Maybe others can provide you more information about that process. Here is a little bit about my path that you might find helpful:
Coming from a design background, I have not have any trouble being accepted into OT programs. For me, the hardest part about getting accepted into OT school has been completing the necessary prerequisites to be eligible to apply to schools. My design degree did not require me to complete many of the science and psychology courses needed by OT schools. I think it took me about 1 1/2 to 2 years to complete the necessary prerequisites. For me, this was because at my community college, biology had to be taken before anatomy. Then, Anatomy had to be taken before Physiology. This is not the case for all colleges, so you might look into colleges where you can maybe take Anatomy and Physiology concurrently to save time. As you can see, however, it can easily become three semesters worth of just science classes before you are even eligible to apply. This does not include any psychology courses or other courses you might need to apply. Also keep in mind, from the impression I've gotten, there is an advantage to having all prerequisites completed before applying to schools.
I think my biggest advice looking back, is that I wish I would have narrowed down my list of OT schools earlier. When you know what schools you want to go to, you can find out what prerequisite classes are required and can map out how you want to take your courses. It also saves you from taking courses you don't need. I didn't look into specific schools until I had finished most of the common requirements for most schools, and I remember looking at some OT schools and deciding I wasn't going to apply because they had one requirement I had not looked at and I did not want to spend more time taking classes to complete that requirement. It was disappointing to have worked so hard to fulfill requirements only to cross some schools of my list because they had a requirement I still did not meet.
I don't know if this helps you any, but if you have more questions, feel free to message me privately and I can answer any questions you have.