Question about Edifier S1000MKII

It is a master/slave concept, whereby only one box is active (= with amplifier) and the 2nd box is only connected to the master box via speaker cable. The audio signal goes to the active box via 2 pairs of cinch sockets. Therefore, 2 audio sources can be connected. All necessary cables are already enclosed and are sufficient in length for direct operation via computer. Attention, speaker cables or speaker connections between both speakers are only equipped with 5-pin DIN plugs, i.e. no terminal connections. - The remote control should always be ready for use, as the optional buttons for volume and sound are located on the back of the speakers.

Yes, with a speaker connection cable.
I'm not sure anymore. but something between 3 & 5m long

Yes. The connection cable is included (without having measured it, approx. 2.5 metres long).