Doing some searches in the forum will bring up a lot of answers to many questions.
I’m not sure about an ocean on the planet you ask but while on any planet you can enter the sanctum and look up to see the planet. Watch it for a while and it will fully rotate around showing everything.
Water/Lava has a source block in like each block. Once removed it is not replaced until regen happens. We cannot pick anything up yet in buckets like Minecraft. There are a few other dynamics with how it works but overall Minecraft stuff has not been implemented. No ETA on when.
There are many gem posts out there… this has a lot of helpful info - MEGA THREAD: Gem Locations (After March 2017 Resource Distribution)