I just got into bonsai this summer. I unfortunately live in an apt as well with a top floor balcony that is north facing. Luckily , because I'm on the top floor all my trees get at least a few hours of direct sunlight. I think you're fine putting a pre-bonsai tree out on your deck. I definitely agree with Shibui, my first pre-bonsai was a trident maple, and it's taken a beating. I've overwatered it, repotted it twice out of season, and generally stressed the heck out of it, and it's fine. I've also fallen for a lot of beginner traps like he mentioned above, I bought a Japanese maple that was grafted, I didn't know it was a graft until later. Also have bought some trees that really didn't have great potential because of limited branches.
I only have one bonsai that came pre-styled in a pot, and found that I get pretty bored. So now I only buy pre-bonsai that I can work on and watch grow. Personally, I'd recommend getting one tree now that you can get familiar with so you can learn about what you like. On the flip side though, you could go get one in the late winter so you can actually work on it in the spring.