Nice work, I like it,
No wisdom here from me, just some comments.
I think we have to take into account many of these gases leave the reaction vessel as they are forming, depending on temperature, concentration, acidity, metals involved, and which of these gases and reactions have formed salts of metals in solution or have depleted in solution, from the reactions involved, many of these reactions further pushing gases out of solution, or forming soluble metal salts in solution, in reality the equations would be much more complicated to write, or explain than in a simple equations.
In solution from your equation of urea and nitrous acid, what I find interesting is after we take away the gases produced we would form some ammonium chloride in our gold chloride solution, when urea was used.
Also the lower batch of equations ("aqua regia nature"), your equation seems to suggest nitric acid reforming in solution, this also would depend on which of these gases are leaving solution, temperature concentration how the metals in solution were reacting with acids and other factors, several of those reactions would occur out of the solution, example NO gas leaving solution into the air above the reaction forming NO2 gas, mixing with humidity in the air to form nitric acid.
Although we can write these equations for a few of the gases and how they react with each other (not considering other reactions in solution or metals), like how urea reacts with HNO2 alone, it is hard to use these equations to show all of what is actually happening in a more complicated solution of metals and several of these reactions happening simultaneously in solution, example we not only have HNO2 and urea in solution but also gold and HCL in solution and other reactions occurring, and several of these gases leaving solutions, and what is happening at different acidity levels or concentrations of solutions, the equations would be very hard to write.
Sucho, you have done a good job of showing how the reaction may occur, keep up the good work, I like it.