Implementing SAP NetWeaver

We are planing to implement SAP Netweaver and I want to find if any body has answer to my questions:

1- Do we have to upgrade to 4.7 or can it be installed on 4.6c?

2- On average how long would it take to implement NetWeaver?

3- Do we have any documents stating the benefits and ROI of NetWeaver?

If anybody can help me, it would be appreciate it. Thank you