"https://ibin.co/1VMer8BBLzMA"
There is no need for a three-gang box (we're not surprised, though, are we, that an architect specified something about which he knows little or nothing?)
Since we can populate a single-gang plate with up to six (6) standard jacks, there is no need to supply such a wide plate.
The answers to your hum question are (1) no, but I wouldn't do it that way, I would keep the power in a physically separated box, or (2) the NEC down here allows a two-gang box as long as there is a special partition in the box to ensure that the high- and low-voltage systems play nicely together.
Here's a slightly outdated (2008) version of the rule:
800.133 Installation of Communications Wires, Cables, and Equipment. (A) Separation from Other Conductors. (1) In Raceways, Cable Trays, Boxes, and Cables. (c) Electric Light, Power, Class 1, Non–Power-Limited Fire Alarm, and Medium-Power Network-Powered Broadband Communications Circuits in Raceways, Compartments, and Boxes.
Communications conductors shall not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm, or medium-power network-powered broadband communications circuits.
Exception No. 1: Where all of the conductors of electric light, power, Class 1, non–power-limited fire alarm, and medium-power network-powered broadband communications circuits are separated from all of the conductors of communications circuits by a permanent barrier or listed divider.
Exception No. 2: Power conductors in outlet boxes, junction boxes, or similar fittings or compartments where such conductors are introduced solely for power supply to communications equipment. The power circuit conductors shall be routed within the enclosure to maintain a minimum of 6 mm (0.25 in.) separation from the communications circuit conductors.
