Is the term "manipulation" still applying with Bitcoin?
In 2017, we've seen lots of market manipulation because at that time, the total market cap of cryptocurrency is much lower than that of it is today. Now it's harder to manipulate the crypto market, and I don't see these companies having the power to manipulate the market.
It still applies but the likelyhood is getting thinner and thinner as the price and marketcap grows. We already saw some examples of this earlier in the year. The most significant being the German Government Bitcoin sell offs. They knew the price would take a hit if they publicly announce it and put fear in the hearts of many Bitcoiners and traders. Blackrock and any of the dominant players in Bitcoin right now might backtrack and you'd see sell-offs that would follow.
Bitcoin manipulation doesn't have to be with money or a lot of money, they can manipulate with news, Fud...As we can easily see the news about Mt.gox, they have been using it to manipulate the market for more than 10 years and it is still effective until now. Market manipulation is sometimes not as complicated as we think, just a few unverified news is enough to make the market panic.
They can sell whatever they want and since they have the power, they can do it, but as long as there will be buyers then everything is good... or is it? 
Yes, definitely. More buyers means more liquidity to absorb the future potential sell pressure. But we don't really need any one org or firm to hold too much of the supply. That alone would spark fear and of course, fud.
What we should be afraid of is the lack of liquidity in the market, not institutions selling bitcoin, it is normal for them to take profits because they need profits like us. If the market always has enough liquidity no matter how much bitcoin they sell then there is nothing to worry about, but if the market is not liquid enough then that would be a worrying sign.