manifold is easy, helps the car to breathe a bit better. to get the full potential, your best off with a de-cat and full system along with a good air filter.
as for throttle bodies, you will only get the best results if you were to fit a cam, have some head work, fit the throttle bodies and have the cars ecu remapped, or for best results you will need to run a standalone ecu setup. this will cost a canny wedge of cash.
you can use bike throttle bodies along with a standalone ecu to save a few pennies on the normal car throttle bodies, but you only get what you pay for.
its easy to fit the manifold and throttle bodies, but you wont be able to set them up, they need to be done by a pro and its will cost you
TBs do sounds awesome, but i would recommend an engine swap to a 16v motor first, then start playing with that. its will work out cheaper in the long run and you can get more bhp