For cosmetics there's no tax, you just need to have a clearance latter or something like that, can't remember.
500pcs can't be declared as personal use. They count as personal use if the cosmetic you ordered is equal to a 1 month usage.
How much is one month usage you wonder, well you can keep wondering, they wont give you the exact amount that can be count as 1 month usage.
Its all up to the pharmacist, he or she will the determine whether your order is equal to 1 month usage or not.

If your item detained by custom, no need to come to KL.
If the parcel is addressed to Penang. Than, KL custom will post it to Penang custom.
Most likely they will send it to the post office near the Ferry. That's where I'd go to pick up my stuff before.

I don't think books are subjected to tax, bought 4 hardcover books amounting to 3kg of weight before and didn't get taxed for it.
Yes, definitely if buy more books can save more on shipping.
You can check the shipping before you make payments.

You might not get taxed but your family might, marked as gift sometimes can get taxed also.
depends on Kastam.

Yupe, depends on their mood. Different kastam officer different protocal.
You can never really tell.
If from personal name and personal address they might let it go but if they feel like charging it, they will ask the receiver to open the packet to see what's inside.