WAS,
AlhamdoLillah Ramzan is going great.
For a 4 to 5 conversion, you just need the gearbox. The existing shifter and lever will work fine. Just a little piece from the gear lever housing needs to be cut, so that the gear lever can move towards extreme right for 5th gear. For any kabli parts involving oils, one must replace the oil, so yes, you have to put 1L of gear oil too.
If the condition of clutch plate, pressure plate and flywheel is not good, I recommend to install a fresh clutch set and tool the flywheel if necessary. For an estimated cost of labor, you can ask any workshop from the contacts at page 3. I think somewhere around Rs.1500~.