Does the effects matter in order such as exhaust over ghost? or does the slow percent prioritze over the speed increase, vice versa?
No, the order doesn't matter, both the slow and boost will be applied. However, the slow will always be more effective, so it's not necessarily worth to pop ghost while exhausted.
From http://leagueoflegends.wikia.com/wiki/Movement_speed, movement speed is calculated by:
Movement Speed = (Base Movement Speed + Flat Movement Bonuses) × (1 + Percentage Movement Bonuses) × Slow Ratio
E.g. if you have 310 base speed, your effective speed with both ghost (27% boost) and exhaust (40% slow) will be:
310 * 1.27 * 0.6 = 236.2
So the order doesn't matter, the end result is always the same. However, the slow is always more effective, because it's a ratio of the effective speed with boosts.
From the example above, normally ghosting would give you
83.7 extra speed, however, if you ghost while exhausted, you gain only
Likewise, being exhausted normally subtracts
124 speed, but being exhausted while ghosting would subtract
Another example; if you slow and boost yourself by an equal amount, say 20%, the net effect would be that you're slowed:
310 * 1.2 * 0.8 = 297.6