I just got back from Nice on July 6! I would be glad to help with questions. Let's start:
1. Kosher restaurants: Nice has 10 restaurants, a pareve bakery that sells meat dishes, a kosher grocery, and a kosher butcher. We went to 3 restaurants. All were a bit pricey, you should know that up front. Also they don't open for dinner till about 7pm
Le Leviathan: Dairy restaurant. Fish, pasta and pizza. We went there for 3 dinners. Pizza is excellent!! Much better than Chicago and even NYV and LA! My mom had the red mullet and salad Nicoise and reported that both were great. My sister and brother both raved about the pasta! I definitely recommend it.
Le Keter: Dairy, ran by Chabad. Pizza, pasta, sandwiches. We went once and it was definitely a mistake. While the food was really good, service absolutely sucked!! we didn't go back
Chez Arthur: Meat. We went twice!! Food was really good and staff were especially friendly. The chicken Caesar Saldana was out of this world!!
We went to grocery twice. Decent selection, prices a but high, which as noted above is typical.
We got baked goods twice. The raspberry tarts are INCREDIBLY AMAZING!! Definitely worth getting. It's 3 or 4 blocks down from Le Leviathan on the sane street.
For breakfast: we got Tropicana OJ from Monoprix, the local supermarket, tomatoes from farmers market, cheese from kosher grocery and French bread at random bakeries. It's pas akum, but the Chief Rabbi of France holds that plain French bread is kosher from any bakery.
3. Where to stay: we planned to stay at the Le Meridien using SpG points. However, we need to rooms for 9 nights, or in other words 18 nights. We only had points to pay for 8 nights. We rented a beach front house from Nice Pebbles realty. While it was a lot more than paying the cash rate for 10 nights at Le Meridien, it was smarter. We got 3 bedrooms, 2.5 baths, kitchen, living room, dining room, and 2 porches overlooking the beach. I checked out the Le Meridien to see what we missed. It was nothing special.
4. Shabbat: Nice has 2 shuls and a Chabad. We didn't go to Chabad but apparently tefillah takes forever there. There was an "Ashkenazi" shul where we went for Shachrit and mincha. We Dave Ed at our rental house Friday night. I put the word Ashkenazi in quotes because the shul had no nusach. They made it up as they went along. They admitted it to us. For example: on Shabbat, there was no birkat kohanim at Shachrit or mussaf. On Sunday morning they did do birkat kohanim.
5. Monaco: you could get there by bus from Nice. We went for about 6 hours and had a great time. We took our rental car there. WARNING: parking is extremely scarce there. If you are coming by car arrive before 10:15am. We went to the Monaco aquarium which was pretty awesome. We wanted to go to the palace as tours are available, but since we were there two days before the princes wedding there were no tours. The palace gardens were open though. It was nothing special but they were beautiful and had breathtaking views of the Meditteranean. We wanted to go to the Casino but we couldn't find parking nearby so we settled for just driving past it. For lunch, we had French bread and deli meat from the kosher butcher.
I will gladly answer questions to best of my ability. Send me a PM or an email.