Anything else I can do to improve efficiency ? Increase range ?
Not really, unless you buy some really expensive equipment.
Instead of using 6 gauge wire, for example, you'd use 2 gauge.
Instead of running at 12V, you'd go with 48V, or 96V (most places going over 100VDC requires special permits or is flat out illegal for DIYers and need EEs to do the work)
Much more efficient buck converter, or inverter, or charger.
Generally speaking, efficiency on power conversion/storage is around 80% on average. You
can get a little higher, but it starts to begin to become dimensioning returns.
You could wire in a toggle switch to reroute power through a boost converter when the battery voltage gets too low for the controller. That way you have no conversion efficiency loss when the battery is above 30% charge
It probably would be easier, cheaper, and more efficient to go with higher string count, 4s instead of 3s, and use buck convertor to run everything. Going with 5 or more in series would be even better.
A buck convertor is far more efficient than a boost convertor. A boost convertor has to use magnetic fields to recreate a higher voltage. This is inherently loosing power during the boosting as a good chunk is dispersed as heat generation.
A buck convertor on the other hand just pulses the power flow and a capacitor to smooth out the output. Think of filling a water tank that has a drain hole. To keep the water at a certain level the valve is either on, or off (no flow regulation in this example with partially open/closed). So to keep a certain amount in the tank, you would turn on the valve until the water line reaches a certain level, then turn off and wait until the power drops to a certain level, and repeat. The output drain would never see a difference.
Running a DC motor would be far better to run it on a buck converter, and just have a beefy enough convertor to handle amps required. There are some out there that can do 50A on the output @ 12V