1)you would be competing against yourself.
You are always competing with yourself, whether you add 300 PH/s or 1 GH/s to the network. That is something that won't change if you add the hash power at a slower rate. There is no advantage to adding it slower from what I can see.
well at the scale of 160ph + 300ph = 460ph
adding 300 ph at 1 watt per hash is quite a task. 1th = 1k-watt 1 ph = 1m-watt
300 ph = 300 megawatt
building the 300 ph in mining gear is not that costly.
having the cooling and the power is harder.
at a certain point large scale mining gear production can be very low cost,
but to run the mining gear you need access to cheap power.
the Niagara Falls power plant usa + can could run 5,000 m watts
that means a plant is build able but how many areas have the right setup to make a 300 m watt plant
the idea that I can make gear cheaply. then add it on as I access power cheaply is not far fetched as some think.
here is a link to Niagara falls power cap.
http://www.niagarafrontier.com/power.html 2700 mw USA + 2300 mw CAN = 5000mw
enough to run 30x the current network if we burn 1 watt per gh
or 15x the current network if we burn 2 watts per gh
If bitfury and bitmaintech get access to 2 cent a kwatt for power in large amounts they will build big places.
Not complicated it will happen.