I want to know if I'll be able to see source if I only use that one or I need to really use the 3 so the source is not ignored
Yes, it will track. They're pretty good at parsing partial data. The more you provide, the better you can slice the data later but anything pretty much goes in.
Yes. I have used Google analytics for the last 10 years and have just tracked the information that I need.
The only *required* field is utm_source. If you do not have utm_source on your tagged links, then the tagging will not work. The other fields are not "required" for GA to work, but they make sense is most cases to use them. At the very least, some form of Source / Medium combination is highly recommended.