A capital letter always starts a sentence.
No, a comma doesn't always follow "however." It depends on the structure of the sentence and how "however" is being used. If "however" appears at the beginning of a sentence, it is typically followed by a comma.
no
Not at the beginning of a sentence. As you know is a clausal sentence adverbial, and as such it should generally be set off by punctuation. That would mean a comma after it at the beginning of a sentence, a comma in front of it at the end of a sentence and commas on both ends when it appears in the middle of a sentence: "He is, as you know, rather obstinate."
No it shouldn't be. Only when it is a beginning of a sentence.
No, a preposition does not have to be found at the beginning of a sentence. It can appear anywhere within a sentence, depending on the structure of the sentence.
No, a subject pronoun does not always have to be at the beginning of a sentence. Subject pronouns typically come at the beginning of a sentence for clarity, but they can also appear after the main verb in certain constructions or for emphasis.
Adverbs can be used at the beginning, middle, or the end of a sentence.
It will almost always be an adverb phrase, followed by a comma. e.g. "In the spring, birds fly south." It can, rarely, be an adjective. e.g. Of (among) the survivors, most were badly injured.
Yes, "midday" is typically not capitalized unless it appears at the beginning of a sentence.
No, except at the beginning of a sentence because it is n ot a proper n ou n.
No, except at the beginning of a sentence because it is n ot a proper n ou n.
When it appears at the beginning of a sentence, or in the title of something. There is no other reason to capitalize it.