First off, congratulations on your new system.
It's a system you should be able to enjoy for quite a while.
To address your questions, let me ask a few more...
How close do you sit to your speakers? How large is the whole listening area? How far away from the walls are the speakers placed? How loud do you like to listen? These will all play into the optimal crossover setting.
Here are the full complement of specs for your front speakers from Polk:
- Total Frequency Response: 60 Hz → 25 Hz
- Nominal Impedance: 8 ohms
- Sensitivity (1 watt @ 1 meter): 91 dB
- Lower and Upper -3dB Limits: 80 Hz → 22 Hz
- Recommended Amplifier Power Per Channel: 20 watts - 150 watts
- Front Array Driver Complement
- (2) 4.5" (11.43 cm) d (Round) - Midrange
- (1) 1" (2.54 cm) d (Round) - Tweeter
So forget about the "Total Frequency Response" spec and look only at the -3 dB limit of the speakers, which is 80 Hz, not 60 Hz. Even this is pretty optimistic with just 4.5" drivers. This 80 Hz spec is measured at 75 dB output. If you like to listen louder than that, (and most of us do), then figure that the -3 dB point will be higher at louder levels. If you sit further away than about 10 to 12 ft. you will want a higher crossover to ensure you don't overdrive the 4.5" drivers. A 100 Hz crossover is certainly reasonable, and you may want to go higher if you listen louder. Just ensure that your 2 subs are not located close to each other so you don't get any sub localization.
Here are the power specs on your receiver:
100 W/Ch (8 Ohms, 20 Hz–20 kHz, 0.08% THD, 2 Channels Driven, FTC)
220 W/Ch (6 Ohms, 1 kHz, 10% THD, 1 Channel Driven)
Note that the 220 wpc spec you quoted is only valid at 6 ohms with a bandwidth-limited, 1 kHz signal, and with 10% Total Harmonic Distortion, (THD, and just 1 channel driven. In other words, you'll never get 220 watts out of that receiver without blowing it up or destroying your speakers.
The other spec, (the FTC spec of 100 watts with a full-band signal and a reasonable distortion level into 2-channels), is much more appropriate and applicable to that receiver. You can expect less output when more channels are driven. Nonetheless, 100 wpc is a a reasonable spec for a receiver to drive those speakers. Having said that, the further away you sit, and the further from the walls the speakers are placed, the higher the demand for watts the receiver will see. If you sit more than 10 or 12 ft. away, you'll want to be more judicious with the Master Volume Control.
Your subs will "see" the entire space, including all adjacent open spaces, as the volume they need to pressurize. 10" woofers in a small box with just 50 watts driving them will be challenged by a large open space. If you can limit the size of the space by closing doors and sealing off adjacent spaces, that would be helpful. Also note that your subs are ported, and the ports are tuned very close to the -3dB point of 40 Hz. If you send them loud signals with content below 40 Hz, they will be especially challenged, and will likely distort and the ports will chuff. You will want to listen carefully to them as you raise the volume to ensure they don't get damaged, especially if your space is large.
Good luck and enjoy your system.