Translation:I open the window.
Jisho tells me 開く is both a transitive and intransitive verb. If this had been 窓が開けます, could it therefore have meant "the window opens" instead of "(someone) opens the window"?
Also, does anyone have any idea how this 開く（あく）differs from 開く（ひらく）in terms of usage?
Grammatically, あく can only be intransitive (the transitive form is あける); ひらく can be either intransitive or transitive.
In terms of the differences in usage, the following links explain the distinctions (the latter one has quite a few usage examples):
An excerpt of the second link:
The translation is both to open the door and there is time when we use them equally. But 開く = ひらく ( = hiraku) is a bit more formal, literal, a bit dramatic and is used when you stress the movement or describe the process of opening something “folded / closed tightly.” or spread something widely.
It also covers some idiomatic uses.
Can this never be "I am opening the window"? I know continuous actions tend to translate into "-teimasu" but is "I'm opening-> akemasu" translation completely wrong?
AFAIK continuous actions MUST be ている, so you would need 開いています to do "opening". 開けます could be "will open" or "open" though, the former which works as an adequate stand in for "I'm opening" depending on the context.
I believe that you could use the Japanese simple present (akemasu) and the English progressive (am opening) in a situation where, e.g., you are standing up and walking to the window while speaking.
Usually, only the context will tell. By which I mean that that sentence could also be about windows. Obviously if you use a number with the word window it will definitely be plural but no change to the word
This seems to be an ongoing issue with assuming subjects without any context. This sentence could refer to anyone and "I' isn't specified in any way here.
The subject could be "I"/"you"/"he"/"she"/"it"/"we"/"they", but the translation does require a subject. Report it.
I was wondering whats the difference of 開け and 開いた? And 開 on it's own also means open (well according to google translate). I'm really confused.