At SST privacy is taken very seriously.
Yes for 100%. Your communication will not be shared with anyone else. There is no NDA needed for that. Email correspondence is going through protonmail which is one of the most secure email providers based in Switzerland. All possible security practices are in place to prevent any email leakage. So yes your communication with SST is private.
Yes. If you feel better that I sign a Non Disclosure Agreement (NDA) when discussing your proprietary trading secrets, that is totally fine with me. Send me the NDA and I will have a look.
No user data is shared, ever.
Emails and attachments are stored on the protonmail servers. Downloaded files from email are stored in Sync folders (Sync is secure storage software I use. Affiliate link here) which are encrypted. The hardware I use has OS level encryption as well. Any backend infrastructure is secured with current cyber security practices. Passwords are strong and 2FA is used on everything. Your data, although minimally present, is well taken care of.