Gotta couple questions...

First..
I can only summon 1 helpful phantom.
Even if there is 10 sign's about the second I summon 1 all the others will disappear.
Is this.. Common?

And second.. I'm debating whether or not to stock all my spare items, equipment, materials etc.
On 1 character and use it as a SL 99 trader for other PS3 folks to use as they need.

You can get 2. Normally they disappear right after you summon your first because the game is working on getting the summon to go through. After that, though, the signs should re-appear.