Not sure if this is too late to help, but after just coming back from Sipadan, my main issue is that the Permit (not the dives) is $90 USD per day to dive Sipadan. Too expensive. I think this is the most expensive dive permit in the world? But people (like me) still come, so, why not keep raising the prices? Also bear in mind this is a permit for 2 dives. Your 3rd dive will be elsewhere.
I stayed with Scuba Junkie in Mabul and had not realized what was making the trip so expensive until I got there. The price SJ is charging for diving and accommodations is really reasonable if not for the permit. But you also don't have to dive Sipdan every day.
For permit availability, I was able to get 5 days of Sipadan permits on a 8 day itinerary with SJ. I don't know how the permit lotto goes anymore, but money and really the desire to dive the same sites many days in a row was the limiter for me.
On a side note there is also a new island that has opened since November for Diving - Seamill. So when you're there you will likely dive Mabul, Kapalan, Sipadan islands. Quite a bit of variety. Seamill is basically a private island, nobody else will be diving there, it is wonderful.
Other things you might want to consider is - why are you going to Sipadan? It may be worth your while to break down what is it that you are expecting to see there.
The signature features at Sipadan are
1. Hammerhead
2. Chevron Barracuda ball
#1 I went to Sipadan 4 days (Ended up switching the 5th day to Seamill for variety) and saw 1 hammerhead at a very far distance that took a quick peek at us and took off. 40-50ft away? 10 second viewing perhaps. Others saw "some", but nobody was seeing a school so I left Sipadan wondering why people are trying to see hammers there when they are more plentiful in other parts of the world.
#2 DMs had not seen the barracuda ball / for several months when we saw it (nevermind if it was in a tornado formation, just did we see them or not?). After reviewing the video, the DM's said it was about 1/2 the size of the "large" ball, so perhaps the school split. Maybe they will group back up some day? But just want to set expectations the % is not very high to see it right now. I saw the cudas 2x in 4 days, the first viewing was a small ball. Perhaps a couple hundred. The larger one was enough to where I couldn't estimate count. 1k? The large viewing was actually not at barracuda point, but in the deep blue at hanging garden.
So ironically for me the things that stand out from the trip are neither of the signatures.
1. seeing +50 devil rays "flying" together as a squadron at Seamil was maybe one of the most majestic wildlife viewings I have ever seen. It's another blue water dive and another couple I befriended went 3 days and never saw them though, you have been warned...
2. 4 pygmy seahorses on 1 fan. We saw pygmies 3 different times (I did ask our DM to see some, non photographers were not super excited about them though...)
3. 4 different ghost pipe fish. Pretty much saw one every other day, aren't they supposed to be rare? :O
4. Huge school of bumphead parrotfish up close. You will see them, the viewing is really cool once you get over the fact that you are swimming in their poop.
5. Tons of variety of sealife in large numbers. Cuttlefish, nudis, octos, crocodile fish, jacks
So is it worth it? What happens out there is a "blue water dive" to see the hammers. This will be dive 1 on every Sipadan day unless you have enough votes on the boat to avoid a blue water dive. It's basically a very deep dive (80-90ft) where you swim out into the blue on a square profile (out, 90deg sideways, 90 degrees back) and see nothing while you wait for a chance to see a hammer.
This part (and the $90/day) I would say are absolutely not worth it to me. The rest of my stay I quite enjoyed.
About your AOW, seems like a separate issue. You absolutely will need to get your AOW to do a deep dive like they will do at Sipadan. I would not recommend getting your cert there, but instead, recommend you do classwork/certs at home or at your normal haunts. Dive and enjoy at the expensive/special places, that is the point of being there right? I just don't see the discount if you are there at one of the top dive places in the world, doing logic puzzles at 90' on the sandy bottom instead of out "diving".
Snorkel vs dive: What are you expecting to see? In general places with current, have wavy top sides. I don't enjoy snorkeling that, but I also don't know where snorkel tours are taking people and what people are trying to see.
