The answers to your questions are as follows....
Sometimes and Sometimes.
Now for some clarification.
GoFerm is used specifically for yeast rehydration or Yeast Starters. It's not a generic "feed"
Many people here use FermaidK and DAP together for their regimen, you can find dozens of discussions on the site about quantities and timings, all up front, or staggered etc. They most of them have expiration dates, and to be honest, in this game, you want all of your ingredients to be fresh and yummy, at the time of use.... I just add my nutrients to my purchase when I need to top them up, whenever I'm at my LHBS or ordering online.
DAP is Diammonium Phosphate, in organic
FermaidK is a nutrient source with vitamins and other yummy stuff for the yeasties, which also contains some DAP.
There's also FermaidO, which is an organic source of nitrogen, that has no DAP, and doesn't yield as much nitrogen as the other sources, which is what I tried to use almost exclusively on my last batch. The theory is, that although you need more of it, so it's more expensive than using the inorganic sources, but unlike DAP, using too much should not impart "off flavours" into the must.
Hope this helps... incidentally, you'll find that nutrients are a constant source of debate here.
I've was looking to get some nutrients so I can make a unflavored traditional mead(water, honey, nutrient).
I was thinking about getting DAP, FERMAX ,fermaid k, GO-FERM in bulk.
So my questions was :
Do DAP, FERMAX ,fermaid k, GO-FERM have some sort of expiration date?
Do I need all of them or are they just alternative to each other?
Cheers Anders