I believe the humpback swimming is mainly done in and around Moorea and not in the Tuamotus but you will have to look into that information elsewhere as I have not done it myself. I also know those activities tend to be booked up well in advance (I myself had to book my humpback swim in Tonga 2 years in advance and looks like it will not be going ahead this year).
I preferred the diving in Fakarava to Rangiroa but didn't have as much luck in seeing the greater variety of animals there as others can - I didn't even get any resident dolphin encounters. I did 3 full days of diving in Rangi and found that to be enough though others could easily spend a week, especially if you are staying at a lovely hotel like the Kia ora and enjoying the sundowner cocktails and pool etc. I dived with 6 passengers and can recommend them. TOP DIVE does not have the best reputation anywhere in FP to my knowledge. The poster above is correct about the dive profiles - given how wide and deep the pass/lagoon is, action can be limited to very deep profiles (the French have pretty strict rules about the type of certification you required to go past 30 metres which is usually a CMAS level 2 or at least a Rescue)
Many will disagree with me but I recommend staying in Fakarava North. You can still get day trips to do double tanks down in the South (the pass there is much more narrow so the sharks are that much more densely populated - technically it is better than the North but the North can still be amazing). The South has limited accommodation options and it is pretty rustic... plus you are isolated from the rest of the island. I enjoyed staying in the North as I could bomb around on a bike to visit the town, check out different snacks, get a massage etc. Also keep in mind when planning that the only way to the South is by boat and if there is inclement weather you could face (days-long) delays in getting there... or vice versa, getting back. Its another reason I decided against staying there and found it was the right choice for me - one of my fellow divers ended up stuck in the North for days trying to get south while I was there... I spent 5 days in Faka and loved it - could have stayed longer though it was purely for the vibes and the relaxation as you exhaust the dive sites after a few days (they are still amazing but really you only have incoming pass dives and then outer reef dives when tides are outgoing which are a bit less exciting). I dove with pretty much all the shops on Faka and can only and highly recommend O2... they were amazing.