Dear Threasher,
(1) I use the IGN map (Google for IGN France). Other popular ones the the Michelin Map. If you're lucky, you can find them at Borders or Kinokuniya, but they are also available at any supermarche in France. Time for you to pick up some French words anyway.
If you have not read my online guide before, please do so:
http://www.comp.nus.edu.sg/~rtan/France/fne.html
(2) For Annecy in 2005, we stayed at:
http://www.accorhotels.com/accorhotels/fichehotel/gb/etp/2547/fiche_hotel.shtml
The price is now EUR 47 per night. But take note that it is quite budget accommodation. For a nicer hotel, try the IBIS range.
(3) Yes, it is convenient, and each metro ticket allows you unlimited transfers; just like in SG. For the prices of a "carnet" of 10 tickets, check this out:
http://www.ratp.info/informer/tarif_ticket_t_plus.php
In fact, in 2005, we stayed near to Porte de Montreuil on Line 9.
But you have to think about it; there is no such thing as cheap and good. The East and North suburbs outside the Boulevard Périphérique (as well as the South to a certain extent) are dodgy areas at night. In daytime it is perfectly fine. You may not feel perfectly safe, though in reality it is not as dangerous as it looks. Just don't come back after it gets dark. But you are Singaporeans who may not have lived abroad before so it may come as shock to you.
I would actually recommend the following ETAP hotel:
http://www.accorhotels.com/accorhotels/fichehotel/gb/etp/5037/fiche_hotel.shtml
It's still in a dodgy area, it costs EUR 54 per night, but it is located right on top of a Carrefour, which makes it very convenient and cheap to get your breakfast and your groceries. It is five minutes walk from the Porte de Montreuil metro station on Line 9. We stayed near there in 2005. My colleague also went there in 2006 and he said it was perfectly fine.
If you want a slightly less dodgy area, consider La Defense at the western end of Line 1. I haven't stayed there before so can't tell you anything more other than the fact that it is a business area.
(4) Yes it is. You're right, it's probably a large station, but I haven't actually been to St Lazare before.
Another thing you should consider: on the day of your departure, how are you going to get to the airport? RER B brings you there in about 30 minutes, but if you have lots of luggage, you would generally want to avoid having to take the metro due to the many stairs (not all stations have escalators) and that you may not be able to look after your luggage adequately since there is only the two of you.
It is for that reason that we stay near the Gare du Nord. It makes departure a lot less of a hassle. Cabs in Paris (as you have already found out in Switzerland) aren't exactly cheap.
But I agree with Peng that if it's your first time, you'd probably want to play it safe.