Installing a USB-A Port on D-Link DIR-300NRU B7 with Ralink RT5350F Chipset
Q1. Is the equipment listed necessary and sufficient? If yes, please kindly proceed to the second question. If no, what is the required equipment?


Yes, that's seems to be the bare minimum required to add a USB port in the existing traces.


  Q2. What capacitor in the point 4 would you recommend to use? What power of the resistor in the point 2 should be installed? Do I have to use zero-ohm resistors and why?


C209 is a non-polarized SMD 0604 or smaller capacitor. If the original mod didn't say, I'm not sure. Try a 0.1uF, that's an average decoupling capacitor. Or look up other router USB mods for their values.

The R129 is just a signal or bootstrap resistor. And originally a smd 0604 or smaller resistor from what I can figure. It's power rating isn't really important. 0604 resistors are 0.1W. A 1/4th Watt through hole resistor would work fine.

The Zero Ohm resistors are jumpers, used to bridge a break in the data pairs or power/ground. It's recommended as the data pairs must be kept the same length or they start to have issues. The jumpers for the power fuse and ground could be bare wire.


  Q3. How should the USB socket be soldered? Which equipment should be soldered into what pins?


A standard usb through hole right angle socket can be soldered in with any regular soldering iron, using typical soldering techniques.