Equipment can help meet the stat requirements of each other?

I believe the rule of thumb is thus:

An equipment cannot use it's own stats to meet it's stat requirement.

An equipment may use any and all other equipments besides itself to reach it's stat requirement.

If it can reach it's stat requirements that way, it in turn will help support the remaining equips, thus keeping them all equipped.

This is exactly true. Doing what you're doing takes a lot of thought to squeeze out every little point available. Most people though who are in the DPS game don't have to worry about this as overall and weapon are the only thing that are class-specific [I think]