The vast majority of your questions can be answered with the Scott US Specialized catalog and the Scott worldwide catalogs. Catalogs a few years old are readily available and very reasonable. I would recommend you invest in these incredibly useful references.
I understand and I became a member to this site to receive opinions, advices and feedbacks from the experts in this site for me to have a better understanding and learn from the experts . Thank you Mara
Is you collecting focus more on the value of you items than their place in the collecting continuum? There is nothing wrong in taking an "Antique Roadshow" approach to our hobby; but, there is much to be appreciated in stamps and covers beyond value. Hope your time on this forum helps you this hobby to its full potential.
The problem is that there are 16 different varieties of this green once cent Benjamin Franklin stamp and they were being printed in vast quantities between 1922 and 1938. They were being used not only during that time but also for a while afterwards and as such they are one of the most common US stamps ever produced. There are a couple of those 16 varieties that can bring some meaningful money but those are so rare that the chances of finding one are about as close to zero as can be. 99.9999 percent of the ones you find would sell for a few cents at most and no dealer would buy them since they have to make a significant profit to cover their operating costs. All of that aside, one should not consider collecting stamps or postal history as a way to make money - in most every case one loses money when one sells their philatelic collection unless one focuses on buying true rarities and pays the money they cost, then puts them into a coherent collection that someone in the future might be willing to pay for. The whole point of collecting stamps and postal history is for the fun of the hobby - to learn about the stamps and to learn about how the mail traveled from the sender to the recipient. To begin to be able to do this a collector needs to invest in buying the relevant catalogs for their area of interest. A beginner can start by going to their local library and looking at such catalogs there, or if one gets specialized then they can ask their local library to seek an interlibrary loan from the American Philatelic Research Library in Pennsylvania to be able to read such books. Soon the collector will want to buy their own copies of the catalogs they find the most useful. Money can be saved by buying used copies, a few years out of date but still having the technical information as then newest editions. The recommendation of the Scott US Specialized Catalog is a good one to start with. One will also need to buy a quality metal perforation gauge and quality lighted magnifying glass for magnification, then eventually things like and ultraviolet light and a color gauge to identify shades of colors.
Reading philatelic literature on the area of interest that you are going collect is important to learn what kinds of markings on covers can enhance their commercial values especially since the stamps used on covers are frequently not much of a factor in the commercial value of covers. Fore example, if you were to have the very minimal value one cent Franklin on the cover you show not on that very minimal value postal history cover instead on a cover of that same era that flew on a Zeppelin, then it would have substantial value, not for the stamp, but for the postal history of how it was used.