Yes that's correct for series wiring.
The input attenuation on the front panel should be maxed out, the AVR LFE trim should be at 0, and the master volume should be set low (at first).
The DSP software gain knob should be at 0 at first.
Then play some music and crank it until you get the correct balance, within the limits of the gear.
The DSP software gain knob should be the first thing you adjust.
Reducing the level is always safe. If you are boosting more than 3db, then adjust both the LFE trim and software gain by equal amounts. Monitoring the input and output levels to make sure nothing is clipping and adjust accordingly.
If you only need to boost a particular frequency range, then use the EQ to do that. Always monitor for clipping in's/out's after making large adjustments using aggressive music/movie scenes, then lower to back to reasonable levels.
Generally a subwoofer should be good for at least 3mm's of excursion before failure is even a physical possibility. Every mm beyond that comes at increased risk (and is highly frequency dependent.)
Ported and Horned subs generally reach max excursion either slightly above or below tuning. It's normal for the excursion to reduce as you near the tuning.
For sealed and IB the excursion increases drastically below 30hz, in a predictable way (until amp roll off, in power or FR).
Playing at the system impedance peak is the safest frequency to play for a given wattage/excursion.
Voltage across a resistance causes current to flow.
Current causes heat. (Like 2x the current is 4x the heat, it's not linear, in gets exponentially worse.)
For a given voltage, lower ohm'ed subs will get hotter faster than high-ohm'ed subs.
For a given wattage, the amount of heat produced will be the same for all ohms. Likewise for amplifier guts.
Most subs, at reasonable distances, should be capable of 90db without too-much trouble.
Every db beyond that comes at increased risk.
Using the box sim and distance law you can predict the safe level.
That said, sim's don't take coil/amplifier heat into consideration.
The UMIK maxes out at 130db, regardless of distance, *if* to do the dip switch adjustment to it. Otherwise it clips much lower in SPL. You have to adjust the sen-factor in the cal file accordingly (so take before and afters to ensure you haven't changed the detected db's. 100hz sinewave at 95db at <6inches should do.)
Then you'll be able to take sweeps up to 120db or so. Beyond that the umik will still register another 10db but genearlly it will be with increasingly gross mic distortion.
You'll know in REW if the mic is clipping because the SPL and RTA window shows 0dbFS and the db's turn red.
As for the inuke, the level monitoring tree is a logarithmic db scale.
So 0db is full power (clipping).
-3db is 50% power
-6db 25% power
-10db 10% power
-20db 1% power
Generally speaking, if things are clipping or getting hot, clacking or going into protect mode, then that is a clear sign that you need to double or quadruple the amount of supporting equipment to handle that playback level safely.
So higher efficiency stuff, bigger cones, more cones, beefier ratings etc.
Most people will be happy with a pair of subs and one amp at first, but then often quickly evolve into a proper basshead, buying dozens each, at a time...
I mean, you're not a real basshead, until you've fried at least 1 DIY sub.