Postdoctoral job search: mixed applications
I rarely find people applying to one job and moving on. Doing so involves a lot of risks. In applying to the one job you believe is best, and getting rejected, you keep delaying the hire date of the job you may get. In waiting for a response from your perfect job,the alternative positions may be filled or closed due to lack of appropriate candidates. Point is, the norm is for people to apply to multiple positions, across universities or departments, or even within the same department or doctoral college.

One person in their search applied for two positions within the same department, both of which he was well suited for; both positions will from here on out be referred to as positions A &amp; B, respectively. The person preferred job A, but for reasons like the ones mentioned above, he applied to both. He was contacted for both positions and was deemed fit for both positions. The supervisors then realized that they had the same candidate; enter inter-departmental politics. Eventually, the supervisor of position A yielded and the person was assigned to position B. The point here being, there exists a possibility that it is no longer your choice which position you take once you apply to multiple positions in the same department/university, less so within the same field.

Also, if you receive an offer for a position less preferred and you accept, do not renege if you receive one for a position you prefer more. Aside from the ethical and moral issues, the person you just harmed will be your colleague in your field for many years to come; i.e. this may also harm you professionally.

As for the last part of your question, you'll find plenty of examples of people that occupy any number of roles as a PhD, lecturer, researcher or post-doc. People also tend to move fluidly between these positions. It's also worth mentioning that it is irregular for a post-doc or researcher to not lecture. This is as the post-doc/researcher requires students to fulfill certain portions of their research. To do so, the post-doc holds a lecture, at least, the moment they begin their work in order to attract students that are interested in his/her work while ensuring that they would research their part of the work while having the necessary foundation in place. This covers a post-doc that wants to lecture. 

In the case of a lecturer that wants to apply for a post-doc position, you're directly in contact with the supervisors and have an insider's insight into their work. If anything, you could create your own post-doc position by attaining approval for supervision from a professor, and then securing your own funding from a funding institution (DARPA, etc.). In short, as far as I've seen, no, it doesn't harm your chances, but rather improves them.

Sorry for the long post. Hope it helps.