[Thanks so much Asivad for your prompt response! I've provided some more information below.
1) This could be an issue for my one previous employer as he is not available at the moment. However, the letter has a definitive start and end date. Do I still need to adjust the letter in your opinion to include the typed date? Current job (one that include up until 'present' will be no problem to adjust.
That should be fine, no changes needed.
2) Does this mean I should simply exclude my high school education from the 'Education History' section? It does ask whether I have "finished high school or any higher education (including university, college or vocational training)?" at the beginning of this section which is why I included it in the first place.
Yes. If you've done ECA for Bachelors and above, stick with those.
3) Noted. I think I'll include it to be safe.
4) Yes, it's an official English copy received directly from my university. It's an electronic copy rather than a scanned original but I'm hoping this is sufficient.
Should be fine. If you still want to tread carefully on this, get the Latin version translated and notarized before uploading all of them (Latin version, notarized translation, English version).
Thanks again for your help. This really means a lot!]