The cores don't serve the same purpose as the M1 cores. M1 is optimized for single thread at the cost of die size (and a bit of power). I don't have exact numbers, but say the apple M1 core takes 1.5x the die area of N2, the you'd get better performance by putting in 1.5x the number of N2 cores.
Digikey pricing is not indicative of actual volume pricing, especially for FPGAs where they are often many times overpriced when buying from distributors. I doubt the board is sold at an loss, probably sold at a small profit, not that's it's really significant for a low volume dev board.
The circulator[1] is an analogous component in rf, it send the incident power from any port down to the next port, so you can take one port to be the bidirectional connection, and it splits the signal into transmit and receive connections.
The trick to doing smd soldering is reflow. On all budget all you need is a hot air gun, if you put solder and flux on the pads manually before placing the components. With a stencil and solder paste you can save the time tinning the pads, and placing a component every few seconds is quite possible. So if you work really hard and quite possibly break your back you can assemble this board in a day :)
[1] https://github.com/LiveContainer/LiveContainer