With shipped eggs you may get a great hatch, an average hatch, or a horrible hatch. You can also get the same hatch rates with gathered eggs but your chances of getting a really bad hatch are a lot less. Your purpose of the first test hatch is to determine if something is wrong with the incubator or your methods. If you get a bad hatch was it due to the shipped eggs or the incubator or your methods? You don't know. So gathered eggs remove one variable, the possible issues with shipped eggs.
If something goes wrong with your incubator, of course having a second one handy can be a good thing. Some people are more risk adverse than others. I only have one and I'm happy to only have one. Many people have multiple incubators. It's not about what I do or my preferences. It's about you and what makes you more comfortable.
You said money is no object. Nothing wrong with getting two, going through the prechecks, split the eggs, and start both incubators at the same time. I do something like that with my broody hatches. When I set eggs under a broody I give her half and start the other half in the incubator. That way, even if something goes wrong with one (almost never does), the hen still has chicks to raise.
When General Eisenhower was selecting which generals he wanted to use, he did not want a general that was right 100% of the time. He wanted a general that could make the right decision based on the information he had on hand and act because you never have 100% of the information. You do not need months to start incubating. If you take more than a week you are dithering. Ike would never put you in charge.
I can tell we are totally different personalities. I like things simple, especially when I'm learning. Some people want things as complicated as they can get, like certain of my relatives. As much as they complain I think they thrive on the drama. Embrace who you are!
With shipped eggs you do not know how old they are or what conditions they were stored in before shipping or what conditions they saw while being shipped. The longer before incubation starts after they are laid, the more hatchability could possibly decline. You may be fine storing the first eggs until the second gets in, you may not.
The ideal conditions to store eggs is around 55 F and high humidity. A newly laid egg can go over two weeks in those conditions with no loss of hatchability. I don't know your circumstances or how you can create those conditions. I store my eggs on my kitchen counter in temperatures in the mid-70's F. Humidity is fairly low. But I only store them a week at most before starting incubation.
Yes. You do not want the cold eggs getting condensation on them when put in a hot humid incubator. That could compromise the protective coating (called bloom) and allow bacteria to enter. That's why you do not want to wash the eggs before incubating.
You can read a lot of threads on this forum where people order from different sources and get problems with shipping times. The first time that happens I sympathize with them, they haven't had the experience to understand the potential problems. The second time that happens I figure they like the drama. That's being harsh though. Sometimes they really want two separate breeds and that is the only way to get them. It's worth the risk to them, though I'd consider a second incubator. As I said, some of us are more risk adverse than others.
I hope you get something useful out of this. You are embarking on an adventure. We do not know how an adventure will end. I wish you luck with yours.