First off get your o2 sensors replaced, atleast the precat ones(though you are advised to change the post ones aswell).
Failing o2 sensors will fool the EMS that your car is running lean and will dump alot more fuel into the engine , giving sluggish performance and lots of other cons aswell.
The cat's in these cars last a lifetime , no need to go spend money on a new manifold before you've replaced the o2's.
As for your symptoms:
1. Tires,driveshaft or any driveline part can do this, most often it's unbalanced tires or a bad wheel bearing (but that would be audible and constant)
Anything you feel or hear at a certain speed is not related to the engine, if it's at a certain RPM then yes it's engine.
2. Camshaft sensor, stock EMS defaults to 360 degree engine cycle instead of 720 degree cycle, meanig alot less performance.
3. FCAB's or your front rotors are bad.
Do this to see if it's the FCAB's (or jack the car up and shake the wheel with your hands at 9 and 3 'o clock, if you can the fcab is bad)
4. Camshaft sensors again.
The B sensor is the exhaust side sensor.
Get yourself one of these :
You'll thank me if you ever do some maintnance on your car