I too am a regular WDW visitor and visitor of DL in California. I visited DLP for the first time in June 2015. Here are some of my thoughts:
Studios Park:
Really there are only 3 major attractions there that I would spend time on, although I hear there is going to be a new show replacing Anamagique and I am a fan of shows so I would probably like it. The the attractions are:
1. Ratatouille: don't miss it, it is one of the best Disney attractions in any park I've been to. If you can't get a fast pass, use single rider unless you must ride with the people you came with.
2. Crush's Coaster: very fun, although it spins so if you have spinning problems (my husband does and couldn't ride)you might need to skip it. This ride also has single rider.
3. Tower of Terror: This attraction is one of my favorites in WDW so it is a must for me everywhere. This version is basically the same as the one in California, which is fun but not as good as WDW's.
Honorable Mention: I liked the Slinky Dog ride in Toy Storyland, and Toy Storyland is worth at least a walk through.
Food at the Studios:
Bistro Chez Remy is a good restaurant to eat at in this park. It is the only place I ate in this park (besides an ice cream). It is well themed and had good food.
Disneyland Parc
It really is too bad that Big THunder will be down while you are there as it is my favorite Big Thunder, but anyway.....Space Mountain was down while I was there but from my understanding it is a lot different than the ones in the USA, it goes upside down. Also Pirates is a lot better than anything in the USA, but I hear they are going to add Jack Sparrow stuff to it, which hopefully doesn't ruin it too much, but it is still a must.
Other Musts (of what is open while you are there): Phantom Manor, Alice's Labyrinth, explore in and under the castle, go through and explore some of the walk throughs including the arcades on Main Street, and Dreams.
Pinocchio, Peter Pan, Snow White are nice but are very similar to Disneyland's in CA, just in French (which was pretty neat to listen to). it's a small world is worth a go too, because I enjoyed the America/North America scene, and because I like small world. We didn't do Casey Jr. or the Storybook Boats, because my husband didn't want to but I hear it is a little different than DL's. There is also the Indiana Jones Roller Coaster, which is okay, nothing compared the Indy ride in DL. But if you like a coaster that goes upside down, and being jostled it is okay. There is some decent theming, but definately not worth a long wait, I'm a big Indy fan so it was a little disappointing (and upside down coasters give me headaches).
Food in Disneyland Parc: Quite honestly I found the quick service here to be terrible, but I didn't try all of them. Toad Hall was passable but Colonel Hathaway's was disgusting (although the theming is pretty cool inside as it was meant to be like the Adventurer's Club originally I guess). We also tried Walt's restaurant and the theming was really cool and the food was good. However the restaurant was really dirty, there was a thick layer of dust on everything in the room we were in and a mousetrap next to us on the floor.
Downtown Disney has a lot of restaurants and is easy enough to get to from the parks. Too bad you didn't have time for Buffalo Bill's Wild West show, it was a highlight for us with a great show and surprisingly decent BBQ food.
I will say that DLP has a distinctly French feel to it (not a bad thing) but just a different vibe than WDW or DL. It was really disappointing that the food was not good, with all the fantastic food we had in Paris it was just a shock that DLP couldn't do better, but you won't starve. Also, we were told (by French people)that since the annual passes are so cheap, there are a decent amount of pick pocketers that work the parks and we did see some suspicious activity. Also at one point my husband's sunglasses case was magically gone when we passed through some people, so I suspect he got pick pocketed (he had been warned), that was an inconvenience for him as they were prescription but he had an extra old pair (that I had to force him to pack in the first place). So don't let your guard down because you are at "Disney".
Overall DLP is a very beautiful park, and it seems like they are currently working really hard to improve it. It is a fun place to visit and the Dreams show at the end of the night is great. Oh and as for transportation, the RER is very easy to use, by a return ticket when you buy your ticket to DLP or when you arrive at the DLP station, then you won't have to worry about it at the end of your night.