We should also learn about the properties of the magic-coins.Can we create small objects out of the same material?
Yes. Mana-sculpting is not an unheard of hobby, but most wizards prefer to practice their craft in other ways.
Would we be able to create a useful knife in an unexpected situation?
I could create a sharp object, but mana does not hold an edge very well, and it isn't something that can be done rapidly.
Can we recall the magic from the coins to replenish our stamina, or reshape the pseudo-material into something else?
Yes, and it is where they get their value from. Reshaing is easier then making more coins, but not by much.
Can it bend, break, tarnish, rust, wear away?
It is quite durable, aside from its poor ability to hold an edge.
Can we move it (the material) with our mind?
Not any easier then a mundane material.
Can other Wizards dispel or steal the magic from them?
They may only be "used" at a very close range, unless the other wizard is extremely powerful. There are rumored to be only three wizards with the talent to offensively drain the coins of an opponent at a respectable range, but they would be unlikely to need it.
Only the bravest of lesser wizards would risk themselves by getting close enough to preform this feat.