If you did purchase either the Vegas Pro or Vegas Post package (but not the Vegas Edit package), then serial numbers and links for Stream and SFA should have been included in your purchase documentation along with Vegas Pro's serial number and links. If you did purchase either of these specific packages and you did not get the extra information, you would need to contact Vegas Support about the matter.
@mike-rawlinson ... Unfortunately, the naming convention of the three Vegas packages is confusing because all three packages include Vegas Pro 19.
The three packages are:
Vegas Edit - which consists of Vegas Pro 19 only.
Vegas Pro - which consists of Vegas Pro 19, Stream and SFAS.
Vegas Post - which consists of Vegas Pro 19, Stream, SFAS, Vegas Effects and Vegas Image.
For clarification of what you purchsed, check the email receipt that would have been sent to you at the time of purchase. Alternatively, go to the My products listing on your MAGIX My Account to see what version of Vegas Pro 19 you have purchased. If it is Vegas Edit (which consists of Vegas Pro 19 only), then Stream and SFAS are not part of that offer.
Sort of.. It is a separate installation. The Sound Forge AS install process can be initiated in VP's installation manager which downloads the program and begins installation. I have no experience with Stream but I would assume the same .. if you did in fact purchase Vegas 'Pro' or 'Post'. As @Dexcon stated, your Sound Forge activation code would be in the same email with the other Vegas serials.