You didn't define who "you" is. If "you" is someone who is your boss, business partner, or if there are more people then you may consider this:

"I hope to hear from you soon"  is roughly: "Upam da se kmalu slišimo" . It is as close I can think it can to technically match your desired sentences.

But you could also say something with a little more native feel like:

"V pričakovanju vašega odziva vas lepo pozdravljam Name Lastname"

Which is roughly:

"In expectation of your reply I, Name Lastname greet you "

If you're addressing person of honor(teacher, manager, someone official or so on) you should write "Vašega", but if you're addressing company or other group of people you should write "vašega". Yes only difference is in capital letter.

If you write in name of your company/company you work for use "pozdravljamo" instead of "pozdravljam".

Great answer, Rainy.  Thank you!

Oh, in Slovene, I mean!