When it comes to the first Tizen phone specs, I've read quite a few times that Samsung will be making its first device a high-end one. Knowing Samsung, they are likely to release a bunch of phones, ranging from low, mid and high end, especially since Tizen is basically their baby, too. Anyway, take that with a grain of salt as it could end up being just rumors. Develop as you usually would with mobile performance/limitations in mind, I guess. Otherwise, you could try out the Tizen emulator in its SDK here.