No tax free between Sweden and Germany. We voted against tax free when we voted for EU membership... so it was gone in 1995 when we joined the EU.
Anyway, if I were you I'd try with only three motors... and even that is too much for your PSU, unless you have one for every motor. 10A is way too small for 4 x 4A, which requires 16A + a margin if you are using switching supply. 2 motors are OK, but three is already too much, four... I would not even dream about.