Does one need to buy daled minim or can he use someone else’s?

Hi can i buy a lulav etrog for someone and give it as a gift?

And can you post the proper procedure for setting up the arba minim – – is it hadasot to right of lulav, aravim to the left?

Kvod harav. Theres a tradition to put the lulav/hadasim/aravot in an entryway in the house,which one would suffice?