How important is the supervisor at masters level?

Hello all,

I am doing a technical masters degree and have to choose a supervisor and a project.

There are some supervisors in our department that are very senior and well renowned for their research. Hence I've been naturally drawn to contact them and attempt to formulate a challenging proposal within their domains of expertise. (They also tend to be busier people).

There is another supervisor in the department who has recently finished their PhD and are an assistant lecturer within the department. They have near to none cited publications in comparison, but are working on a project that interests me.

I would like to apply a particular technique to solve some of the work within this project, although I believe this supervisor would be of much help, there are other lecturers/supervisors within the department who would perhaps be able to better advise me on the application of this particular technique.

First question: Would it be inappropriate (or even rude) to seek help from other professors during the course of the project?

Second question: How important is the supervisor anyway at the masters level? Should I factor in the supervisor over the project application domain...

... considering that we work on the project for about 7 months (fully over the summer period). I understand at PhD level the supervisor can make or break your doctoral, but what about at a Masters level?

Any views here would be much appreciated. Thanks in advance.