Hi
1) What would the total price be?
MyShopping just helps you to buy the Software by comparing prices offered by the top rated Software stores online in Australia.
Read "What Is Myshopping": www.myshopping.com.au/2B--whatismyshopping
Please, ask about shipping your "online store"
2) can the asus f3e-ap183e be downgraded to an xp os?
Yes, it can be.
3) how much to add another 3 Gb RAM?
See it
www.myshopping.com.au/PT--66_Random_Access_Memory_RAM_Laptops__fs_12280_e__At the time of writing it would be about $60 - $70, but memory prices move quickly.