On the what percentage do you need question,
If you get 50% + 1 share, you can call an EGM or at the AGM vote for who you want on board and put up your own candidates for the board, this gives you almost total control of the company. The rights of minority investors are respected as the company still is listed on the Stock Exchange.
At a level of 75% of the shares the bidder can take the company private
At a level of 90% of the outstanding shares When the bid is announced the remaining shares can be compulsorily purchased. In the case of Aer Lingus Ryanair had 16% when the bid was announced so they need 90% of 84%, this is an aditional 75.6% meaning if or when Ryanair hits 91.6% they can force the remaining shareholders to sell.
These are the UK rules, the Irish ones may be slightly different (Ihave seen reference to only 80% being required.
The other way is by a scheme of arrangement, and it could work like this, Ryaniar get 50.1% then appoint whoever they want to the board. The Board (Ryanair chaps now) then reccomends a scheme to shareholders, and if 75% agree company is taken over and delisted. More Takeovers are being done this way now, it is more difficult if it is a hostile takeover(as this is), but a possible way to get full ownership of a company with only 75% of the shareholders on side.
My personal view, Ryanair got the 16% by having financial institutions buy shares on it's behalf when the company was floated, the extra few percent were mopped up from a couple of buyers who are out for a quick buck, the major institutional investors think there is more value in the company and Ryanair will increase it's offer this week or next and Ryan will end up with around the 40% mark fairly soon, this gives them effective control of the company, as another 10% will vote with whatever Ryanair wants, but don't want to sell to them, they want to ride the gravy train of Aer Lingus with MOL in charge.