Re filling Scalia's seat, I can easily see a scenario whereby no one gets nominated or confirmed this presidential term. Assuming the Democrats win the presidency in November but only barely gain a majority in the Senate one could see a 4-4 split for the foreseeable future. (In a 4-4 split the decision of the Circuit Appeals court being appealed holds sway *for that circuit only* so you could have different decisions in different circuits becoming the law.) Even with a Democratic president and majority in the Senate the Republicans could filibuster any nomination. (Or vice-versa if the Republicans should win the White House.)
If one of the liberal justices were to resign or die, that would create a 4-3 split, but still leaving the possibility of filibusters preventing any new nominations being approved for several years or until the Senate has a filibuster-proof majority. Nothing says we have to have 9 justices. It was originally six but has varied from seven (1807) to nine (1837) to ten (1867) then again to seven (1866) and back to nine (1869). Congress decides on the size. How this plays out will be fascinating to watch.
Note that while a recess appointment has been done before, most notably by Eisenhower (William Brennan) and the president has the authority under Article II, National Labor Relations Board v. Noel Canning redefined slightly what was meant by "recess" (you know when the children - Congress -- go out to play). Whether anyone would want to be nominated that way is problematic since the appointment is only temporary and would have to be confirmed after the session.
Of course it must be remembered that a vast majority of SCOTUS decisions are unanimous, (it hit a record high during the 2014 term) over 65% and that the decisions that split on ideological lines are very small. Only 14% were 5-4 and of those only 10 were ideological splits.