Generating Electricity Using a Steam Turbine and Small Motor
Whether a BLDC motor is used as a motor, or as a generator, the shaft speed is related to voltage, shaft torque is related to current, and mechanical power to electrical power.

If you spin the shaft of a BLDC motor and follow it with a full bridge 3 phase rectifier (6 diodes), you will get a DC voltage source, voltage proportional to spin speed of the motor, from which you can draw a current with your load. As you draw more current, the BLDC will throw more braking torque onto your turbine. The load determines how much current is drawn.

If you're driving a load directly, it's most efficient (electrically) to use a DC to DC converter to get to the constant low voltage you want. If charging batteries, then get a battery charger that runs from a low DC voltage. Using an inverter up to mains voltage, then running mains input chargers will work, and while less efficient than staying with LV DC, may well be more flexible. 

There are lots of modules available on eBay that step DC up or down, to adjustable voltages from a wide range of voltages, look for 'DC-DC converter'. These will often be 80-90% efficient, so able to supply 5v at 2A while drawing no more than 1.25A, and maybe as little as 1.1A from a 10v supply.

My major concern is the speed of the two devices. The turbine claims to run up to 20krpm, and I would expect it to provide reasonable power and efficiency only at the upper end of its speed range. While the motor does not appear to have a max speed spec, its kv*max_volts is only 9380rpm. Direct coupling at even 9k rpm could be quite exciting unless you are a skilled model engineer. There are at least 4 reasons you don't want to run the motor too fast, bursting, balance, air losses, and electrical efficiency. A toothed belt reduction drive from one to the other would provide both gearing down and mechanical isolation. An outrunner motor tends to be higher torque and lower speed than the equivalent inrunner, there might be higher speed motors you can choose if you do want to drive directly.

How much electrical power do you want to provide? You have chosen a 330W rated motor. While it's a good idea to have a motor rating several times higher than the power you want to draw, 10x higher is probably overkill, though that will give you plenty of capacity in hand if you want to draw more power later.