My bike had an e-line on it when I bought it, so I can't' answer the questions about installation. It does look pretty easy, I assume you have to remove the stock flywheel. You would also have to wire the lights up - not sure how much of the wiring is included and how much is custom. Much of the wiring and light mounts on my bike appear custom. Easy stuff, but takes some time to plan and do.
Also not sure about added weight - but e-line should be able to tell you that.
I can say it is a really cool mod that works great! Mine is wired with an 80 watt headlamp, tail light & brake light that come on when the light is switched to high beam, and the other 100 watt lead goes to a set of grip heaters.
The e-line is reported to smooth out low end power. Again, never rode my bike stock, but it has extremely linear power down low.