You need a lot of bitcoins or money to do that
Do you mean "money or fiat"?
I think whichever would be fine since you can always exchange. But true, you would need alot. However, woudln't the people with ALOT of btc also be the ones who would benefit the most from this kind of price manipulation.
Yeah I think so, traditionally it's always been when someone "corners the market" in a certain commodity that they manipulate the price up by withholding large amounts of the commodity. This seems hard because there's so much BTC.