If you read through the DLP forum, you will get almost all of your questions answered.
Disneylandparis.com is also in English and will give you all the information you need about current prices and specials they have running (the cost goes up and down, unlike the US parks).
Best option - get a passe partoute ticket, which is the equivalent of a park hopper. You can preorder your tickets from disneylandparis.com, or you can buy them in several locations around Paris. THey are not available in US Disney stores. You should know that as an American, you will not be eligible for any of the special ticket rates you might see advertised around Paris for the locals. THey have reduced ticket prices to try to get Parisians into the park. THere are no ticket discounters for tickets for anyone from any other country.
As two adults with no kids, Depending on what time of year you go you can do everything in both parks in one day, or it could take two days to do everything you want to do at peak. THe parks are much much smaller compared to the US parks, but at peak times get just as many people crammed in there so the lines can be atrocious.
Read through my other DLP posts and you will get lots of good information about which rides to do first, etc.
Are you going to DLP just for the park? Or are you going to Paris and building DLP into your routine?
DLP is about 30 miles east of Paris. I highly suggest getting a hotel in Paris and doing the RER commute to DLP (40 minutes by train) rather than staying on Disney property, unless you want not to immerse yourself in any French at all, and just want to do the Disney thing. Paris Metro subway and RER express are very efficient, safe, and fast. DLP is in Zone 5, so make sure you get Zone 5 tickets or passes.
I go to Paris about 4 times a year, and build in a trip to DLP two or three times per year. Avoid peak - anything between June and late August, and weekends APril through OCtober. Other than that, the crowds are manageable. Paris crowds are different from US crowds. They don't line up, they just mob an attraction, and there is severe line jumping. EVerything is more manageable off peak.
THere is not as much to do at either of the parks as there is in the US parks - even merchandising is limited so you don't have that same "pass the time in the shops" kind of thing going on.
If you stay at DLP in one of their resorts, they do have Disney Village, which is comprised of about a dozen shops and restaurants and nothing like Downtown Disney - but the Europeans staying at the resorts flock there in the evening. Most Americans and Brits head into Paris at night.
I can't emphasize reading through the DLP forum enough - you will find many many answers to your questions.
One final caveat -- do NOT get the book Unofficial Guide to Disneyland Paris -- it is completely outdated, and the information is just plain wrong throughout the guidebook.
talking of which :wave: