I believe this is similar to "an apple" in English. It is a matter of phonetics. It sounds better when you use the "n" to connect the "a" to the word apple. The same thing would apply to "e" and "ed" in Italian. The "ed" would make a smoother connection.

There is no difference, you have to use "e" in front of a word starting with a consonant, "ed" in front of a word starting with another "e", if the word start with a vowel that isn't "e" you can chose which one to use. The same happens to the prepositions "a" and "ad" and can happens, on your choice, for the conjunction "o": "od". The "d" is called 'euphonic d', its aim is to avoid two vowel sounds in sequence, and for the "e" and for the "a" (not for the "o") it also has an etymological meaning because they come respectively from the Latin words "et" and "ad".

Yes, they both mean " and" in english. You do use " e " if the next word begins with a consonant and " ed " if the next word begins with a vocal. Andare e venire, Soccorrere ed aiutare.

both means "and"; we use "ed" when the next word begins with vocal