How much time would it take to learn Megilla layning to the level of a pro with zero prior layning experience?
I've been a Torah reader for about 45 years, and have read Megilla for about 20 years. This is tough to give you an exact assessment, here, because there are several factors here. So, take what I write as my own "best professional" opinion.
I'm going to assume throughout that you can both read and pronounce Hebrew well. (I've been listening to numerous Bar Mitzvah boys in my shul that can't, but some of them are reading the maftir and haftarah and are butchering everything. So, pardon, my having to state the assumption, but I hope I'm right. If not, then my estimates are going to be way off.)
Most Bar Mitzvah boys do spend a year learning their parsha. I agree that it's way too long for most assuming that your diligent. That means that you need to practice your notes and parsha about once per week. An average parsha is about 100 verses. If you practice once per week, I think a competent musically inclined person could do a competent job in about 6-8 months assuming no prior knowledge.
My method, though, is "unconventional". Most Bar Mitzvah teachers start by teaching each individual trope sound and trope "groups" and have students practice and review this for 2 - 3 weeks. It's nice to know the theory, and it can't hurt. But, I have found that many Bar Mitvah boys are nervous / stressed by the Bar Mitzvah itself (much of this is really the parents' fault, BTW) and focusing on this can be more frustrating than it's worth. Even for adults that will lain, occasionally, this can be useful, but it's unnecessary. You can learn the parsha like you're learning a song without even knowing the names of the notes.
The Megilla is a constant. The words never and trope never change from one year to the next. Also, it's the only trope "mode" of its kind. (I.e., Torah trope sounds one way, haftara another way, and its "portable" to multiple parshiot.) So, in short, the learning method for Megilla is the same as for Torah. Learn it like a song (i.e., don't waste your time on what each trope sounds like, unless that interests or helps you.)
Now extrapolate the time estimate above. The Megilla has about 200 verses. Now, I'm not suggesting that it will take you double the time as learning a Torah parsha, but it might. Offhand, I think that if you review a chapter once per week, you should be able to do it in about 8 months.
Some factors that will affect this time:
- Your musical inclination / ear / competency. You don't have to have a stellar voice, but you definitely can't be completely tone deaf either. The better you can memorize the sound, tone, nuances, the quicker it will be.
- How good is your memory for music and word pronunciations? The Megillah has both the longest verses in Tanac"h (that does make it quite challenging) as well as some of the more unusual "tough" pronouncing words in Tanac"h.
- How much time can you review and how frequently? Obviously, the more frequently you practice the quicker things will go. But, you must practice frequently, because it's easy to forget what you did if you don't.
- What's your stamina and determination? You will make many mistakes at the beginning, especially, as well as throughout this venture. If you're the type of person that gets easily frustrated and gives up ... well, my friend, maybe this venture isn't for you.
I strongly encourage you to learn from a competent Ba'al Kri'a, but most of all someone who is extremely patient and someone who encourages and believes in your competence. This is a tough project for a beginner to do on his own. There are various tapes / CDs and online resources. But, none of them will either correct you or give you useful criticism, which is really what you will need.
Another method you can use - but you really need a good musical ear. I learned Torah laining mainly by attending shul weekly and following along with the Chumash and listening to my shul's professional Ba'al Kri'a (Torah reader.) I focused on a set of trope notes and picked up the sound and rhythm by listening to the reading. In my case, by the time I was taking Bar Mitzvah lessons with the Ba'al Kri'a and my parents and neighbors said I needed about 8 months, the Ba'al Kri'ah heard me and said I needed about 3 months. Alas, few shuls now use a hired reader who is the same one each week, so this may pose a challengs. But, if you have a good musical ear, you can do it this way.
Megilla won't be as quick because it's read just twice per year. But, you could, technically, learn it from a tape / CD if you have a sharp musical ear. It's not for everyone, obviously.
I hope all this info helps. Best of luck.