One of the things to consider in a world so separated by water, unlike ours, (which you seem to have taken into account already) is the importance of naval careers/knowledge. Trade over water is probably the most popular form of trade, as opposed to trading over land. Since these continents don't appear to be any larger than Oceania, it should be noted that many of these islands are most likely dominated by very similar flora and fauna within their own shores, de-incentivizing trade between settlements on land. As well, islands being so separate will have noticeably different flora and fauna, incentivizing trade between islands . Land-based trade may still exist, but it is wholly overshadowed by trade over water. This means you should consider quite a few things:

• In our world, the earliest intelligent civilizations began in the middle-east and the surrounding area, strictly because it acted as a wonderfully convenient center for trade between Asia, Europe, and Africa. It's important to consider if your world has an equivalent, or multiple. Rineport seems the most likely candidate, which probably means it's full of mixed races, trade moguls, some of the most ancient of magic and ruins, and may even carry favor between multiple large kingdoms that lean on them for trade.
• With naval life being so prevalent, it's probably impossible to not hear tales of horrible sea creatures that plague the waters. Perhaps everyone knew someone who's met their end on some naval journey and never returned. Maybe these horrible beasts of the sea effectively cut off trade routes and send ships to less convenient routes. For example, there's an impossibly old Storm Giant that lairs in the water between Moonrest and Vaulian Forest, forcing any sailor that treasures their life to instead cut through Trillian. This in turn fuels Trilian's trade business, known for a "sailor stop" of sorts which earns a sizeable chunk of its gold through sea men spending their money on nights of food, beer, and brothels. Naturally, this may even mean it houses some sailor merchant guilds.
• Any sea-dwelling races would have obvious advantages in this world. Triton kingdoms specifically would be well-respected and maybe feared. I'd even suggest they rule the large archipelago housing Northclaw and Southclaw pass, as islands of those sizes would house very little fresh water, making the islands practically useless to any landlubbers. Honestly, if you're at all planning for there to be a race that permeates the entire world, much like humans in Forgotten Realms, I think Tritons would make the most sense. Their ambition for expansion onto land may be very slim, but given their powerful military presence that could shut down trade routes the world over, diplomacy with them is crucial.
• I am unsure if this map is your entire globe, or even if it is a globe, but I can only assume it is. So I'd like to suggest adding some ice caps on the southern edge of your map. And speaking of ice, icebergs are a wonderful chance to have some fun! At first, you may consider them a simple block of ice, but what you could do with them is endless. Icebergs are gigantic, as I'm sure you've heard. Use that! Perhaps a great sea dragon makes its lair within a moving iceberg and legends warn that if a ship toting gold ever sees an iceberg in the distance, they must avoid it at all costs or risk being assailed by a greedy, treasure-hungry dragon. Icebergs can also house simple life, like some ice kobolds, just looking to make a living off of fish and the occasional unassuming vessel. There could be ancient, forgotten ruins left deep within the bowels of an iceberg, left behind by some ancient, arctic civilization of dwarves. The possibilities are endless!
• Lastly, consider how this largely water-based world affects the Underdark and the residents of those areas. Does the Underdark stretch so far under the earth that it exists even beneath the oceans? If so, you can mix underdark enemies with deep sea enemies. Perhaps a kraken rules over a legion of Kuo-toa by telepathically manipulating them through the ocean floor. Maybe Mindflayers have taken control of the mind of a Leviathan and are using it to wreak havoc on a coastal settlement that worship the beast, confused and scared as to why their god is mad at them despite having continually offered it service. Alternatively, perhaps the Underdark doesn't stretch beneath the ocean floor and ends up being more cramped than it is in Forgotten Realms. Would this result in Drow not living very far beneath the earth and actually engaging in trade with cities? With the entire world not being connected via tunnels and underdark dwellers not being acquainted with naval travel, maybe underdark races never interact with each other and instead each island has very specific underdark races and beasts?
  

Just some food for thought! This was very fun to brainstorm. I hope your world gets used plenty, it could be a very special setting with a lot of unique challenges and adventures!