1. "Well-meaning" and "well-meant" are both the same concept and they are both adjectives, but you will use them with different types of nouns. This is because they carry the idea of an intention, and a thing cannot have intention. So, you will use "well-meaning" to modify the person with the intent. And you will use "well-meant" to modify the thing that was done.
My well-meaning friend shoveled snow off my sidewalk, but uncovered a layer of ice in the process.
My friend performed the well-meant gesture of shoveling my sidewalk.
2. "Intention" is a noun. But the phrase here is "well-intentioned" it is a phrase that is an adjective. "Intentioned" on its own is not a word that is used much. (I've never heard it.)
My well-intentioned friend shoveled the snow off my sidewalk.