As I know it depend first on the matrix in which you want to reinforce CNT.
Second the size of CNT can affect majorly the dispersion in matrix.
If you are mixing it in any polymer then you can use both king of filler sizes. But if you want to mix it in metal matrix composite, then there is a chance of agglomeration after a wt.% of increment in CNT in case of fibre form, and less possibility of agglomeration in powder form.
Binder:
Thermoplastic based PMC : phenyltrimethoxysilane (PTMS)
It actually depends on which matrix you want to reinforce your CNTs with. You can use Epoxy as your matrix and with this you can process your nanotubes in powder form with the matrix. This can be solution -processed when you disperse your nanotubes in appropriate solvent.