Watch out for the heat efficiency. The viper cooks pretty quick and having the overcharged power plant with monstered plus the four overcharged multicannons (with mostly incendiary) will limit how much the ship can shoot. Switching to an armored power plant with thermal spread will bump the heat down a bit.
Don't worry about getting as much power as possible from the power plant. The ship just needs enough to not be over 100% and you can also assign module priorities to turn off the FSD and cargo hatch when hardpoints are deployed.
If it's really combat focused you might also be able to get away with a smaller FSD. That would bump the speed up a bit and lower the power draw. It drops about 10ly to go to 3D so not great for longer travels but there's no fuel scoop equipped anyway. If it's really not going to travel it could do a 2D FSD with 1C fuel tank too but this might be heresy
If you find that the two extra overcharged multis are still generating too much heat you could try dumbfire missiles. They have a tricky learning curve but with penetrator munitions from Liz the ship can really start punching above its weight. You can take out multiple big ships like anacondas and corvettes with a tiny viper which is super fun! I've heard that dumbfires are good for bombing ground bases too.