Good is an adjective - well is an adverb. The word well can be an adjective as well as an adverb. In some phrases well is used as an adverb and in others it functions as an adjective.
So, you have to state what do you want to describe. Adjective is being used when describing a noun, and adverb when describing a verb.
About prepositions (in, at, to, etc.)- A preposition links nouns, pronouns and phrases to other words in a sentence. The word or phrase that the preposition introduces is called the object of the preposition.
But I am not sure what you are asking-What about using prepositions?
About commas: Use commas to separate independent clauses when they are joined by any of these seven coordinating conjunctions: and, but, for, or, nor, so, yet.
And, again, I am not sure what do you mean: When starting a sentence, do I use Well, I would like…or today, I will be discussing. (?!)