Yes, the reward is 1 SP per block.
You can have multiple accounts in one instance of the software, miners/witnesses, however if you use multiple witness accounts the rewards will be split among them as whichever witness signs a block gets the reward.
i must create accs at first? or use random free usern and create key https://bitaddress.org/
New accounts can automatically be ceated upon successfully mining/witnessing of a block with the WIF private key you set them to use, they can use the same key as your main account that you already have.
Just make sure first that you set a name that is not already in use, most people just add some numbers at their main account for additional ones. You can take a look at the miner-witness queue on steemd.com for an idea...