This でな is indeed the te-form of だ, followed by な, a masculine sentence-final particle.
A sentence-end で can have several different roles. Here, it may be a reason marker (i.e., explaining to someone why he has a sweet), in which case the combination of で + な roughly corresponds to "you know" in English. Or it may be a simple "continuation marker". As this ...
It's from old 山の手言葉. ざます/ざぁます/ざんす used to be actively used in the past among classy madams in Yamanote regions, but today it's used mainly in fiction as role language of snobbish people and nouveau riche (usually middle-aged or older).
The most famous user of ざます in fiction is probably Suneo's mother.
じょ used to be a very common sentence-ender in Awa (Tokushima) dialect, although it's becoming obsolete, like other dialects. Looks like じぇ is a sentence-ender in Iwate dialect.
That being said, this character's speech is not dialectal at all, so basically this is just another unique キャラ語尾 used to add flavor to a character.
Some キャラ語尾 are "recycled" ones ...
Final particles (ね, よ, な, さ) can be thrown in the middle of a sentence in conversation as if fillers.
There are technically two types:
follows the first word/chunk of the sentence
それがね、本物のマツタケなんです That one, see, is the real matsutake.
もしもね、ゾンビに襲われたら If, I mean if, you're attacked by zombies...
It is used to emphasize and draw hearer's attention. This can ...
Given the limited context, there's only so much room for interpretation, but assuming that this is only a fragment of the conversation, this can be an acceptable answer.
そうですね is a way to say, that is so or right, but there are also cases where it is used as the speaker is gathering their thoughts about the matter. While not expressly stated in most ...
This な is a masculine filler particle meaning nothing. If you know ね, さ or よ used like this, this な works the same way.
Examples of filler-な:
What is the にはな used for in the following sentence?
Meaning of triple particle (?) のはな
What do 「はな」 and 「いうとな」 mean?
What does さあ (saa) mean?
Use of さ as a filler
Spaces in children's books
This type of ほう is used to make the sentence sound euphemistic and/or courteous. According to 明鏡国語辞典第2版:
So 準備のほうを is a milder/politer equivalent of 準備を, and the omitted verb is simply してください or しなさい. Maybe Sunako used ほう because she knew she was going to interrupt Ayane.
This type ...
As far as lyrics are concerned, in the Japanese culture, the original lyrics are never modified even when they are sung by someone of the opposite sex. If the original lyrics say わよ, a male singer sing them as わよ. That's not strange at all, and no one thinks he is gay. (In English-speaking cultures, this may not be true. You can see "his" changed to "her", ...
Explanatory-の is a very big topic and it's impossible to cover everything in a single question, but your explanation seems OK to me for the most part. But let me comment on some of your statements.
You'd rather say なにしてる？ rather than なにしてるの？ and that applies basically to any question.
I'm not sure what you mean by "genuine", but "なにしてる?" sounds fairly ...
Please forget より for now. より for "comparison" is used in the context of more ～ than ～, as in "He is taller than me" or "It's more expensive". To say "like ～" or "similar to ～", you have to use a completely different construction. You can use:
I don't like ...
Here の is used in the same manner as you might こと, as a nominalizer(sp?)
It is common to end a sentence with ことだ or のだ basically turning the sentence structure into " it is the case(thing) that ..."
Effectively there is little difference in the meaning than if it was not there at all, but it can have connotations of politeness, so for instance in ...
I think it's a mix of the two: a "dialectical" (or perhaps just personal) "pronounce ぞ/ぜ as じょ/じぇ" thing (but only specifically for the sentence-ending particles).
I feel like, in fictional media like video games, manga, and anime, sentence-enders are the very first thing that gets "tweaked" to indicate some sort of dialectical or individual, quirky ...