ZaraUbermensch

Does CircusEditor have a way to add a line break or did you have to paste it in another way?
For the 91xx remapping, I used a hex editor to add a 0x91 byte in front of each accented letter. This was easy to do manually since it's just one or two sentences for my example text.
I started with typing it as regular text, viewed as codepage-1252
   Olá, este é um teste Add a 91 byte in for each accented letter, viewed as sjis
   Ol黛, este 鷹 um teste Convert the remaining letters to full-width in sjis
   Ｏｌ黛，　ｅｓｔｅ　鷹　ｕｍ　ｔｅｓｔｅ ...and then paste the resulting text into the script. It should be possible to automate the procedure above for your translation. One way would be to add support for remapping accented letters within CircusEditor -- it is open-source.
My dll also remaps the full-width alphabet back to ASCII so the letters look normal instead of  ｗｉｄｅ  in the game, and it was usually necessary when non-Japanese fonts don't have support for sjis codepoints.

Accented characters: The square symbols is probably because the character was misinterpreted as something else by the font. What tool are you using to edit the game's MES files? This will ultimately need to be customized to work appropriately with whatever way you're handling accented letters in your script + font.
When I did accented letters for my example, I essentially remapped accented symbols to the 91xx SJIS range and the dll would map them back to the intended codepoint. For example, ê is 0xEA in unicode/cp1252 and outputted as 91EA in the script file.
Line breaks: the game expects the script to provide explicit line breaks in the text using the 0A byte. That means your editing tool needs to be able to insert line breaks into the text; the game will not auto-break lines by itself.

Most of the font overrides I did were handled with a dll that I wrote. Here's my current one for it, just put it in the same folder as the game exe.
Finally, the text spacing is a hex edit on the exe. Since I did my testing on the disc release of EXS, these next instructions will only work for that version.
Use a hex editor and look at address 1CA32 in the exe, and you should see the bytes A1 B8 52 BB 00 ..... now overwrite those with B8 0C 00 00 00 where 0C is the amount of spacing. Something between 09 and 0C should suffice, depending on the font.
I should mention that a bunch of technical considerations will need to be kept in mind, but I'll let you try it first and see how that goes.

A VN's font is usually embedded in the exe itself. You'd have to dig around in the exe with a decompiler to find the font and even then you may or may not be able to replace it and still have the VN run properly.

The font name can be found in the exe (in this case, it is ＭＳ 明朝) which can be patched via a hex edit, or overridden with other means. But that's the easy part.
For Portuguese, you also need to have some way to use accented letters, which is something not natively supported in SJIS encoding. There are some ways to handle that, such as an edited font, or patching in support to the exe.
This game's engine doesn't accept normal ASCII text in the script, so you're forced to use full-width letters which  ｍａｋｅｓ　ｅｖｅｒｙｔｈｉｎｇ　ｌｏｏｋ　ｗｉｄｅ in the game. That also can be fixed by patching the exe, which seems to have a hardcoded amount for the text's letter spacing.
A decent looking starting point could look like this. The new font being used here is Comic Sans MS, of course.