Haven't been on here for a while (busy with school and applications). Good to be back!
Now on to your question . . .
First of all congratulations on the move to Paris! And the Latin Quarter is great - that's where I lived and I wouldn't do it any differently. I'm sure you'll have a fantastic time!
Now in terms of do I wish I had known anything in particular before I got there. No not really. I had done my homework but nonetheless there were things that shocked me:
1) I expected French bureaucracy to be bad but I had no idea just how bad!!!! If while you are there you have to go the prefecture to get a Carte de Sejour I wish you luck. Be prepared to bring photocopies of absolutely everything. EVEN the stuff they didn't ask for. The French love their red-tape --- you've been warned!
2) I was not prepared for their banking services and financial transactions. I found myself in a place where at times people wouldn't take visa and interact was often out of the question. A direct deposit? Forget about it!!! Banking fees are so extra-ordinarily high in France that many transactions are often complicated as a result.
Oh and don't be surprised if people don't give you receipts. Many places don't - not sure why.
3) Rudeness and a general lack of customer service is an issue. Parisians are special. That's the way I like to put it. Yes, it can be a HUGE turn-off at times. Especially on days when nothing is going right. But it's just something you live with.
4) This is a big one: THE BUSES IN PARIS ARE OFTEN BETTER THAN THE METRO!!! I didn't discover this one until very late on in my stay. For example, I was at the Luxembourg RER and to get to some parts of the Marais I had to switch lines several times. Included the dreaded switch at Chatelet - Les Halles. You can walk for kilometres just to switch lines at that station and the platforms themselves will often smell like urine. That and that's one place where you should becareful with your bags.
One day I took the bus and was so surprised at how ridiculously quick and efficient it was. Not only that but you have the added pleasure of the fantastic sights out your window. It's spectacular! And since you are in the 5th/6th to go almost anywhere you have to pass the Seine. Glorious I tell you!
Ummmm......... just looked at your profile and realized you are female. That means I have some stuff to add to this.
The men in Paris can at times be SUPER agressive! And I completely highlight super. This is particularly the case in the hotter months of the year.
My friends and I have been randomly groped many a time. It is not rare to be followed by blocks and harrasment is a serious issue! It got to be so ridiculous that we basically didn't trust any male we hadn't met in class. I even got picked-up and harrassed at church.
Now this has to do a lot with the attitude of a lot of North American women. We tend to be friendly and might smile at a sales person or something and heaven forbid but we often notice what's going on around us. I had to learn to walk into a store really serious (that kept the guys at GAP from making any more suggestive comments about a room in the back for me) and I learnt to basically ignore everyone around me when I went to the Metro. It worked but it definitely was an adjustment. I'd just suggest that you becareful as they can be overly agressive at times.
And lastly about your blowdryer. The Paris equivalent of K-Mart/Walmart is Monoprix. It's actually more up-market than either one but it's the equivalent in the city. They also have a store in Montparnasse called INNO which is owned by them but also incorporates a supermarket. You'll be able to find your blow dryer at Monoprix!
Oh and if you happen to go outside of the city you will also find places like Carrefour. They are more like Walmarts but don't exist in the city proper - mainly 'cause they are "big surfaces" and take-up a lot of room.
I hope I didn't scare you here. Just trying to be honest. Now having said all of that I still wouldn't trade in my experience in Paris for anything in the world! In fact since I got back I often find myself wishing I could pop back for a visit or even to live there again (later on of course).
And the Latin Quarter in particular I loved - I'm all about the Left Bank!
Best of luck planning your trip and PLEASE don't hesitate to ask anymore questions. I promise to try to answer ASAP.
Cheers!