Basically, you're confusing this: If you are saying "Uno", it because it's numeric, like the number 1, or you're refering to yourself (but don't get mixed up with this reference to yourself stuff). You only use "uno" as the number (uno, dos, tres, cuatro). Thing is, when it's femenine, you use "Una", because "Un" it's only used for "masculine" things. For example, you never say "Uno sol", you say "Un sol"; it's like saying "A sun", "A tree", you are defining a single generic item. Let me know if it is confusing, I have no problem in trying to make it better for you :)

Well, you actually are not saying "uno" for the second list. "Una" is the singular feminine definite article, while "un" is the singular masculine definite article. "Uno", as far as I know is just used for the number, one.

"Un and uno" are indefinite articles, this means that those articles are talking about something not known or can not be identified. Un - uno = masculine singular. My brother is a "teacher", we aren't explaining his teaching specialty, we are simply telling what is his profession. My brother is "one of the best teachers." We are making a special emphasis on a quality. It means that he stands out among several teachers.

"Un y uno", son artículos indefinidos, esto quiere decir que son aquellos artículos que hablan de algo no conocido o que no se puede identificar. Un - uno = masculino, singular. Mi hermano es "un profesor", no estamos explicando cuál es su especialidad de enseñanza, simplemente estamos contando cuál es su profesión. Mi hermano es "uno de los mejores profesores". Estamos haciendo un énfasis especial a una cualidad. Quiere decir, que él se destaca entre varios profesores. I hope that it can be a good explanation for you.