Is their obligation for a Shul to have a Rabbi? What are the needs/roles for/of a Shul Rabbi? We are a small shul, most people coming here where part of a larger Shul before and ask their questions to their senior Rabbis, additionally when a Halachic Question comes up in Shul, we consult a senior Rabbi.

ב"ה Shalom, Before I answer, first allow me to say that whatever I write here is to assist you to formulate an opinion about the job of a Rav for a shul. But obviously if there is a community discussion on this issue, it is not my intention to get involved and that has to be resolved through peaceful community discussion. Secondly, my assumption is that you live in Israel, where all the religious services, meaning: Kashrut, marriage, eruv, mikveh, burial after 120 years etc. are all provided by the local religious council whereas in Chutz La'aretz, the local Shul Rabbi or Rabbis are the ones who handle all there issues. In Chutz La'aretZ, therefore this question wouldn't arise for anyone who wants to live a Torah way of life where he or she lives. However, in Eretz Yisrael, where all the religious services are provided, without a Rabbi, we shouldn't think that a Rabbi is not needed. In my opinion, a Rabbi is a lot more than the religious services but he is needed in a shul from a spiritual point of view and a practical point of view. From the spiritual point of view , the Rabbi through his personality and example , his relationship with the community and its members, his lessons and talks is supposed to outline a path for the community to follow and to strive for. From the practical point of, the Rabbi is the one who answers individual's questions in Halacha, and of course community questions which arise in regard to the custom the Shul should follow especially when people came from many different places previously. This can prevent many disputes in Shul. Especially since you described a situation where senior Rabbis are consulted, this should not create a situation in which some people side with one senior Rabbi and others with another . In a case in which one senior rabbi is agreed upon, it solves some of the issues, but you still do not have somebody who is a spiritual leader for the community. A Rabbi is the one who gives Shiurim and talks in Torah to teach, guide and influence. Certain functions of the Rav may change from place to place according to the needs and character of the community. All the best