I get how the navigation would work but do we have an understanding of their supply situation? How did they travel with enough fresh water due long voyages? How many people/boats would go out at a time?
Any reading recommendations on the topic would be greatly appreciated.
First the recommended reading. There is quite a bit on the topic but the best on to answer your question will be Bellwood's "Man's conquest of the Pacific."
I think the navigating is probably the most interesting part, but since you already understand that part I will start with fresh water.
There are two primary sources of people in the Pacific (to leave out Negritos), the people who can from the SE Asia subcontinent Sunda (the Papuans and Australian Aboriginals) and the Austronesians. The Austronesians spread South from Taiwan about 5k years ago. They reached the Bismarch archipeligo around 3.5kya. This particular group of Austronesians is called the Oceanic peoples, the Oceanic languages are a subgroup within Austronesian. The Oceanic peoples developed a distinctive form of pottery called Lapita, which has been found throughout Melanesia. While this particular form of pottery was likely used more symbolically (gift to neighboring chief etc) it does suggest that pottery was available for hauling water in wayfinding missions. This form of pottery was preserved up until Fiji, which continued the practice even after it was lost by the Polynesians. This is worth noting, because the Polynesian did the most extreme exploring of the Asutronesian descendents. The Polynesian likely abandoned pottery making because they didn't find the right type of clay, but even modern hula has large hollow gourds, this is, of course, the next reasonable water vessel as well.
One of the keys to being able to carry lots of supplies on long sea expeditions was the switch from the outrigger canoe to the double hulled canoe, a Polynesian innovation. The double hulled canoe could carry lots of supplies and you could even build a little shack on top to get out of the elements.
Your other questions are of course more difficult to answer, archeology can only reconstruct so much and numbers of ships that left at one time is not one of them.
I have recommended Bellwood already but I also recommend:
Blust "The Austronesian Languages" (this is free online) Oliver "Native Cultures of the Pacific"
Of course, you're always welcome to check out r/austronesian
Edit: autocorrect typos outright to outrigger
While waiting for an answer to your specific questions about logistics, you may be interested in this excellent overview by u/TheFairyGuineaPig from several months ago.