I plan on putting a system of 3-4 stereo speaker pairs to listen to music at moderate volume levels in my backyard for background music when barbecuing or lounging by the pool.

Specifically, what kind of receiver will work to power multiple sets of speakers at moderate volume level. (I've heard more speakers at lower volume works better than a few speakers that have to be louder and create loud pockets).

Also, I'd prefer if my kid ever finds the volume knob and cranks it up, it doesn't blow the speakers or fry the power amp. As a bonus it wouldn't get ridiculously loud (e.g., over 110dB) and piss off my neighbors.

I'm thinking of getting using pairs of rock-shaped outdoor speakers that are 40W nominal, 80W max, 8 ohm impedance (though not tied to these), 87 dB sensitivity (at 1 W) with an outdoor volume knob (100W) (also available at 50W/75W) that has jumper settings to match the impedance of multiple speakers wired in parallel. (I am open to other suggestions if someone knows of better options for speakers).

Question (1) roughly how much wattage do I need for the receiver?

Doing the calculations myself, if I went with a 50 W per stereo channel amplifier like a DTA-120 or SMSL SA50 (50Wx2), I think I'd have 12.5 W per speaker which at the quoted sensitivity of 87 dB at 1W means it should go up 98 dB = (3.01dB * log2(12.5) 87 dB), which is plenty loud. However, I'm wondering would sound quality at lower volumes improve if I got a more powerful amp?

Question (2), if my amp is providing 50W per channel, should I get a 50W volume knob (e.g., does 100W in volume knob mean 100W per channel or 100 W total)?

Question (3), if I opt for 3 pairs of speakers initially, does it make more sense to use the jumper setting for 2x or 4x on the volume knob? (E.g., as the overall impedance of three 8 ohm speakers in parallel is 2.67 ohms, is it better to give my input receiver 5.33 ohms or 10.66 ohms? I'm guessing 5.33 ohms, but not 100% sure.)