CFE is a business tax which you are exempt from for the first 3 years, although this is being extended until this gov decides what they are going to do with the AE regime…You can pay on line and this is always at the end of each trimestre, the same for everyone regardless of when your business was started, so end Jan for 4 th quarter end April for 1st quarter, end July for 2nd and end Oct for 3rd. You declare even if your return is nothing. That way you keep your Carte Vitale rights.
If you check www.startbusinessinfrance.com there is a lot on the CFE. As an AE you are exempt from this for four years. It is essentially a business premises tax. You do need to fill on the initial form however. I pay it every year and it varies depending on where you live. The site above will also give you a draft letter you can send should the tax office send you a demand by accident next year.
Sorry I can't remember what the CFE bit is. The main thing to pay is quarterly social charges to RSI. The bill for this last quarter will arrive in January and you pay that by the end of January. The first quarter bill will arrive in April and so forth. I do not pay online, I send cheque in post. One thing I would say is that they are very strict so make sure they get payment by due date.
Go talk to your tax inspector, they are usually helpful. Go with somebody who speaks French.
good luck