Had you been a subscriber to the LeLingo.fr bilingual helpline you could have got an instant answer to your questions by telephone and a full confirmation by email. Here are some answers to your questions which I hope will be useful:
Deposit (Caution): In French law the deposit on a furnished property (meublé) is not regulated at all as it would be if it was unfurnished. It is up to the landlord what he asks. The common practice deposit is indeed TWO MONTHS, usually paid along with the first months rent. That means you have to put down the equivalent of three months when you take over the property - two months as security deposit and one months rent in advance.
Etat des Lieux: This is a very important document but it is only part of the story! In fact you need to agree TWO DOCUMENTS with the landlord. An inventory (inventaire) AND an état des lieux. Sometimes these can be combined but it is very important how they are drafted, and how they are signed by both parties with a mentioned copy (e.g. fait en deux exemplaires, etc.) to each.
You have received advice from someone on here to "take hundreds of photos" and attach them to the "état des lieux". The "état des lieux" is a very important document and you should take great care to get it right, to protect yourself and the landlord in the future.
Apart from the practicalities of actually printing them, hundreds of of photos on their own, attached to the document(s) are of little use in law, unless each one is described, numbered and listed in the "états des lieux document and each one is initialed and dated by all the parties on all copies. There is a better way of doing this.
In practice, once you have done the inventaire, which should include absolutely everything you are taking charge of, including the heating and hot water system, wall plugs, light switches, everything listed and described, then you can usually include a detail of the condition of each item (e.g. état neuf, bonne, mauvaise, etc.) and you only need to highlight - and photograph - things that have problems, scratches, bad paint, cracks, broken handle, chipped bath, etc.and put them into the document.
Actually this is probably a bit too complicated to describe fully here. The safest way to do this, which cannot be challenged by either party, is to get an Huissier de Justice to do the état des lieux, but you will have to pay for this. You can ask a huissier for a devis before you start. The advantage is that it is a sworn document which will stand up as fact in any court of law in France.
On a small apartment it should not be too difficult to do this all properly. If you would like some further advice or help then please contact me privately. You will find my contact details on my profile.