Yep, you can. I do it all the time :) -Qué envío? -La carta. Envíasela ahora. -A quién?. -A Luis. Envíala a Luis. :)

you can remove "se" if you write the noun, for example: "envíale la carta a Luis" replacing "envíasela a Luis"

If the person to whom you are talking knows the thing you are talking about, you ahve to use "enviásela/envíasela" (depending if you talk with "tú" or "vos") and if the person to whom you are talking doesn't know the thing you are talking about, you have to use "envíale/enviale".

Yes, you can say " enviala" is used for a place or the other thing like hour.

yes you can if the other person know about the person and where he will send it