There is so little information about the early years of the company, and as far as I know, no surviving records of machine serial numbers in reference to the year of manufacture. Your best bet would be if someone happens to have original documentation for a machine, and honestly, I would love to hear about that as well. A friend and I were just talking the other day about how interesting it would be to know the history of our machines: date of manufacture, original purchaser, etc.
#2 and 3 needles are pretty large, and would not be used for general harness work. A #4 needle was the most common size used for general work, as evidenced by the scarcity of original needles in that size. #5 needles would be used for a little lighter work, while #6 and 7 for very fine work with light thread. New needles are available that will work in the machine, but they are somewhat different than the originals, and require some modification for heavier work. The top part of the shank diameter is smaller than the originals, and will more easily pull out of the machine in heavy work. It's not a good thing when that happens.
I have two original lamps for the Landis #1 machines, and a couple of my machines still have the boilers on them. Once people quit using had wax, the boiler was something that could be dispensed with to reduce weight when moving the machine. There were small wax pots that were factory made for solution wax, and attached to the left of the tension plates under the bolt that goes through the pressure foot spring.
My dear, you have no idea how deep that rabbit hole is!!