I would look at SpectraLogic’s T50e Tape library. Very reliable and modular system which can grow as your environment grows (pay as you grow). They are capable of utilizing LTO-5 which has way bigger capacity compared to LTO-3.
Here’s a link for you to review.
As per backup software, you would want a product that’s is able to stream data multiple to speed up the backup. Majority of the players would include are Symantec’s NetBackup, EMC’s Legato Networker, and CommVault’s Simpana.
Here’s links for them: