If you are using the TK or branch (ha! see what I did there?) then there should already be a Source folder, in which case to get a .sln file all you need to do is right click the .uproject file and click “Generate Visual Studio project files”.
But there is nothing wrong with “Add Code to Project” 
you only need to use that method when there is no Source folder though.
To get multiple planes working you would have to modify the material to use regular parameters instead of the collection parameters, then edit the BP accordingly (that on itself would probably take hours).
But let me save you the trouble right now and tell you that you will not achieve the results you are looking for by doing that
Not only the buoyancy will not work right but also the planes will not blend together properly if they have different parameters… not to mention the performance will go down significantly since there will be multiple gerstner wave cluster calculations.
If you are making a single player game then I would try changing the wave direction in the manager over time, depending on the player’s location.
If you are making multiplayer… you could try modifying each wave set’s “rotation” parameter to make the waves more “chaotic” and move into multiple directions to hopefully make it look less obvious, I have no idea how well that would work though so don’t blame me if you waste your time 
In a perfect world we would want a mix of FFT, gerstner waves and some kind of flow map so we can transition/fade the waves near the shore while keeping everything as mathematical as possible so we can calculate buoyancy on the CPU.
But that is pretty challenging to say the least, if even possible
No idea… it’s not easy to tell what is going on from an error log we need more info.
What are you trying to do exactly? package the game? compile the code? what steps are you taking exactly?
Hey ! glad to hear you are feeling better 