Yes, definitely true of Russian - you don't always get the gender-appropriate speaker. Sometimes a male speaker uses feminine first person past tense - I'm sure the reverse must sometimes be true too. Quite confusing initially, when you think: "I thought only a woman would/could say that!". Although it does teach you to pay attention to exactly what is said, and not to guess, based on the gender of the speaker!
It's "nun" that stands for the sound "n". So the pronunciation is "ani". Here's more on "nun" http://www.hebrew4christians.com/Grammar/Unit_One/Aleph-Bet/Nun/nun.html
The hebrew language has Niqqud (lock it up on wiki). Children learn to read with these symbols, and later on they are removed. There is supposed to be a dot (hirik) bellow the alef to point out this is an "i" sound. אבא for example, has a "patah" bellow it to indicate an "a" sound.
Many vowels in Hebrew do not appear in the spelling. Here א is theoretically a glottal stop - Hebrew speakers would occasionally pronounce it and more often would pronounce nothing. Then there is a "ee" vowel which does not appear at all in this common spelling (there is the alternate spelling אימא which reveals it).
Yes, I had (still have) the same problem, of trying to recognise whole words, without knowing the sounds. In case you don't know about them already, course contributor Mazzorano has set up some excellent external Memrise courses that help you familiarise yourself with the sounds. The first is the Hebrew alphabet, and corresponding sounds: http://www.memrise.com/course/1087087/hebrew-alef-bet/
The other is all the words that feature in the Duolingo course, so you can actually hear them individually (the Duolingo course itself does not have audio for every combination of words, as you know): http://www.memrise.com/course/1031737/hebrew-duolingo/
I personally think the Memrise courses, or at least the alphabet one, should be required learning before anyone embarks on the full Duolingo course, as it quickly becomes very frustrating otherwise.
I found the only downside is that Memrise stopped prompting me to practise after a couple of days, and I've reached the point my Duolingo progress can't go much further without it. I realise that's purely a matter of self-discipline, and I shouldn't need a daily prompt, but the reality is that my Hebrew has pretty much fallen by the wayside, at just Level 4, because it's losing ground to the languages (Dutch and Russian) I don't need external resources for. I'm sure it's just coincidence, but even Duolingo has ceased prompting me about Hebrew (I didn't turn notifications off). Has it worked out I'm a hopeless case? ;)
I wouldn't have thought it was possible to learn a language that way. Especially Hebrew. Some words have no direct English equivalent (for example direct object marker את) If you can remember the sounds of the 26 letters of English (and their many many variant pronunciations) then the 22 of Hebrew shouldn't be a problem. You'll find it hard, if not impossible later on, if you don't have at least that foundation.
I see that the answer square is using Mum, the British spelling this time.
Contradictory to English, A verb is not necessary for all sentences in Hebrew. Hence, the translation of verbs between the languages can be confusing. This sentence, for example, is loosely translated into "I mom". The "am" required in English does not exist here.
The closet parallel verb I can think of is אהיה (a-he-ye) on all its forms (called buildings in Hebrew). For example, "Be calm" - היה רגוע (he-ye ra-gu-ah), "I will be there" אני אהיה שם (Ah-ni A-he-ye Sham), "everithing will be fine" הכל יהיה בסדר (ha-kol iy-hi-ye be-se-der).