I assume you were referring to me as I think I am the only Kenny here. There is Ken who is the owner so if you were referring to him, I'm sorry you have to settle for me.
Let me start with the nitrogen. This does nothing to prevent leaks. The only thing is does is due to it being a different gas, it is not as susceptible to pressure changes due to temperature changes. So we all have seen when it gets cold that the air pressure light comes on because the pressure dropped. The tire didn't lose air it just lost pressure due to the temp. Nitrogen is not a drastic so the pressure remains more consistent.
As for doing two tires at time, that is fine since your vehicle is not an all wheel drive vehicle. However, I would never do just one tire. I would do two tires on the same axle. Meaning both fronts or both rears. In fact, I would look at all four tires and picked the best 2 and put them on the rear of the vehicle. Then put the two new tires up front.
Then when you go to buy 2 more in the future, rotate the tires from the front to the rear and put those two new ones on the front.
As for different brands, it is not that big of a deal but I would try to stay with the same tire. If you happen to get two of one brand and two of another, keep them on the same axle. So the front should match each other and the rear should match each other.
The only reason you can get away with this is, again, you have a 2WD vehicle.
As for where to buy them, there is no one answer because companies always have sales so you will just have to shop around. With President's day coming (assuming you are in the USA) you should be able to find a deal.
Hopefully I answered your questions. Let me know if I missed something.
Saturday, February 8th, 2020 AT 3:22 PM