Japanese naturalization

I want to confirm if I can still retain my original name after naturalization.

Context: Non-anglophonic name with

1 surname (9 English characters, 5 characters in kana)

0 middle names

But 3 first names (5-7-6 characters in English, 4-5-4 in kana)

Problem

Part A: Since I don’t have a driving license, Koseki will be the main certificate in Japan. I could confirm that Koseki can’t have the English character name or any spaces between the names, it will be katakanized, and the first name will be ONE long 4+5+4=13 characters long.

It’s not any different from my current situation when I apply for a bank account, or apply for a credit card with just 1 long kana name. So, even though it’s unrealistically long, there are situations where there’s (1) a character number limit, (2) prohibition from using characters like 「ー」、「ッ」、「ヴ」 that exist in my name.

Part B: It was mentioned to me on the call with the passport centre that, on the passport, they anglicize the name according to the one written in Koseki. However, they do accept 非ヘボン式 names in the passport for people with foreign origin or someone with some level of 実績 with that version.

(3) That being said, I could not get a confident YES whether spaces could be allowed within my first names.

Sorry for the long detailed question. I already tried calling the 法務局、市役所、パースポートセンター but they gave me vague and even contradictory answers sometimes. Anyone who could answer the above 3 questions would reallllllly help me out. I don’t have a particular problem with having my name changed, but the updating my old certificates in the country I was born is LITERAL hell, and genuinely trying my best to stick to the name I was born with.