So if space wasn't an issue, should I just put it in a mylar sleeve and or between paper and just leave it?
I do it different ways and never had any issues
1) just lay each one flat on top of the other. just don't slide the top one against the one below as the linen is an abrasive
2) use some type of paper between each. this can be kraft paper or any other type, depending on how much time it will be stored. the longer the storage specification, the more you you move towards deacidified stock
3) I most often use a one sheet plastic bag as a separator. Note that I do not ever under circumstance store flat posters inside a bag unless it also has a board. without a board, every time you handle the poster you will leave some measure of handling defect behind, no matter how careful you are