Prof. Zdzislaw Zygulski wrote a lot about it (there was hard discussion between him and western experts which disagreed with him saying it's not Polish rider, but he proved it) so I can search notes about it, to not repeating that what was said before. I read about it long time ago, and I just don't remember, but isn't it rider called Lisowczyk
?. This was light cavalry under the command of colonel Lisowski, which during Polish-Russian war occupied Moscow with Polish army in 1610? - I'll check it.
It's a sabre not koncerz under the leg. I'm, not sure for now if Rembrandt wanted to put it there. Koncerz, as I wrote it earlier, was under left leg.
Radu, your Polish is sehr gut
. The only problem is the lack of Polish letters. Arrows you can write strzaly
is singular. The saber is szabla
and this war-hammer is nadziak
. And I wouldn't be so convinced about mustache - it's a young boy anyway, and I didn't hear about sticked hairs in 17th c. Poland