I'm not sure if I need upgrade and use workspaces.

[Joe Phoenix]

I'm not sure if I need a workspaces.

We all have separate Trello boards and I guess I would like to know if we can all still be added to each other's cards, as well transfer cards to each other's boards and if so, do I need to upgrade or is the free version suitable for me? We only use Trello to communicate information back and forth between users, so again in my situation I'm not sure what the need for workspaces would be for?

[Rasmus Wulff Jensen]

Every Trello Board is in a workspace (you can't have a board without one). But it sounds like you more or less have a workspace per Board right now. 

You can stay on a free plan as long as each workspace/board has less than 10 members... (Aka you only need to pay if one or more boards contains more than 10 members)