The way I set mine up was...
Cargo hatch is always off...this saves you 5% right off the bat.
I set the fuel scoop and interdictor to priority 4. I set the warrant scanner to priority 3.
When I deploy weapons, usually those 3 things automatically turn off. If I switch to a firegroup with only the warrant scanner loaded, it will reactivate.
With the shield cell rebalance, it might not even be possible for the viper to use railguns anymore. I have to test that out.
In fact, shield cells might not even be worth it anymore. Will be interesting to see if it's too big a headache.
The first time I pimped out my viper, I didn't know anything about power management. I interdicted an Asp, deployed weapons, then.......brrrrrrrrrr, everything shut down. It was embarrassing. :\
I'd definitely advise dropping out of super cruise in a nowhere section of space and testing it out.