Do pc assemblers usually keep pc assembled in bulk from before to sell or assemble as they get order?

Both methods are used. The more you can pre-assemble, the faster your time from order to ship, though. So places like Dell will have the accessories already bundled together in one box. Then they'll have the case and motherboard already mounted for the most popular processor types. That way they just pop in the memory, hard disk, video card, and any peripherals and box the whole thing up. To cut costs down to a minimum, you keep every component in it's most granular form. That way nothing is wasted and you never have to take the components apart to scavenge. The trick is to find the balance between shipping time and efficiency versus cost and time to manufacture. I would suggest motherboard and cases put together, everything else leave as components. It's easy to install a processor after the motherboard is mounted.

First now you market or potential market then make some models for show so the customer can see what you have, then be honest that will take you to eternity and give you customer good support, and remenber that the internet market it is global, some people can have the luxury that have the best gaming rig and others they will satisfy by have one with windows98, and in most of the world a cheap laptop with wirelles capabilities will make wonders, they most live in rural aereas where cable and some times satelite it is not available.

Assemble as they get order.