"which is the best vSAN solution to choose where each host has 12 TB storage"
Which licensing edition of vSAN you require depends on what features you want/require e.g. if you want to use Dedupe&Compression then Advanced licensing is required, if this is a Hybrid configuration then you won't be able to use Dedupe&Compression anyway so Standard edition should suffice.
What vSphere licensing edition is required is also a 'it depends what you needs' - vSAN is agnostic of this and runs on any licensing edition of vSphere (and comes with free vDS).
"Do I buy vSAN and vSphere separately or there is a package that includes both of them that I can get?"
T180985 "No you dont need to buy seperate licences" - Sorry but this is incorrect.
vSphere/ESXi licensing is separate from vSAN licensing and these are required in addition to each other. While there are/were some packages that contain both (e.g. HCI Acceleration kit and IIRC one other vCloud license) I do not see any of these currently available in the VMware online store and thus you would probably have to contact our sales team or go through a 3rd-party vendor to acquire these.
Thank you for the helpful feedback. Also, I noticed the vSAN Licence editions are not available on the vmware store (https://store.vmware.com/). So how do I go about buying the license for a vSAN standard edition.
Your question was already answered:
"I do not see any of these currently available in the VMware online store and thus you would probably have to contact our sales team or go through a 3rd-party vendor to acquire these."