Sounds like you have a lot of research ahead of you before you jump into setting up a tank. A lot of personal choices goes into set up, so I'd strongly suggest that you do a lot of info-finding, product reviews before moving forward. You need to acquire the knowledge so you can make choices. Good to ask questions, but in the end you are the one needs to make the good choices.
A very good beginning book would be "The Conscientious Marine Aquarist". It pretty much has info on every topic with setup, fish tank types, equipment, animals, etc.
Start by what you mentioned, substrate for your tank. You will be wanting to get sand (do not get crushed coral under any circumstances). I'd suggest dry sand to fill the bottom, but with some live sand that will top off a one inch surface. There are all kinds of choices. For a reef, I'd go with finer sand rather than getting larger-grain sands. If you have a dedicated local marine fish store, see what they may have in stock after you do some online research.
I've used CaribSea sands and they are a very good choice. As an example of variety, here is their website with pictures of types of sand varieties.
https://caribsea.com/aquarium/#