well first of all, i'm not an expert or so... but since i've done the engine overhaul of my santro, i think i may be able to contribute here.... I might be able to answer some of your questions here...
What you suggestion during Engine Overhauling ?
Get it overhauled when it starts giving off white smoke.. If you notice drop in oil level in absence of white smoke, it may be some other reason.. to make sure that you need engine overhaul, you gotta get a compression test first.
What is important to take care during this process?
Try to use a good mechanic (especially a good kharadia) and genuine parts ofcourse. Overhaul is something you do not do everyday so make sure you pitch it right...
Which of Parts are more important to be replace or have need more Attention
Oil Pump, Clutch Plate and Pressure Plate, pistons, rings, bore
What is meanings that Camshaft nosing or weak ? How mechanic can be made Judgement of it ?
If the rotation of a camshaft is not perfect, it might produce horizontal or vertical movements resulting in some tik tik noise (more or less like that of tappets). a kharadia usually fixes it.
Why Mechanic said Bore is to done in Engine. what is meaning of Bore in Engine ?
If the engine is opened for overhaul for the very first time in its life, it's overhaul is done usually by replacing rings, in second overhaul, it'll get bigger pistons with bigger bore (a kharadia literally bores the engine block for a bigger holes to make room for bigger pistons), in third overhaul new rings, in fourth overhaul, new bigger pistons plus new bore (bigger bore), then new rings or Sleeves and the process starts all over.
If you need further information like pricing of parts and overall pricing impact int he complete overhaul, please check-out page 40 of this forum. i've posted some info there...