Yes
Not exactly. Some additional explanation I guess needed
Difficulty is related to the hashrate power of the rig and at the same time the difficulty cannot be arbitrary (it changes 5000/2500/1250 downwards). For example, the difficlty of 2500MH can be agreed to get a rig with 120 MH/s and a rig with 200MH/s (figures are only for example), with this number of shares, of course, will be different, but the difficulty will be the same for two rigs)