Please Help Structuring Db For Future Expansion

first thing's first... i've never set up a Access db. I have, however, worked with php/mysql so I understand dbs and the basic principles behind them.
i was hoping you could help me set up my db to accomplish my goals now and help me in the future when i want to make this system more advanced.

the purpose of the database is to track the 'stages' of several different projects as well as keep account of which contacts are involved.

example

I have projects A, B, C
I have contacts I, II, III
the stages of the projects are 1, 2, 3

I already have these tables (projects, contaces, stages)

the first issue is, i dont know how to assign mutltiple contacts for specific projects
i.e. project A involves I, II, and III while project B only involves I and III. I would like a form to have a listbox with all the contacts in it and i could hold ctrl and select mutiple contacts for a specific project

the second issue... i would like to db to store dates of when a specific project moves from stage 1 to stage 2 for instance. i know i can set up fields in the projects table for these, but what happens when i add a new stage? will i need to go into the projects table and add a new field? can i make this dynamic?


i hope this makes sense to you. if you could give me direction, i would greatly appreciate it. before doing something that i will regret later, i hope you can give me some tips based on your experiences.

thanks in advance.