

Of course they collect content you upload. How else do you think they maintain a chat history so people can see what was said while they were offline?
I see nothing in the privacy policy that says they can sell the data. There is, however, things that allow them to share the data with 3rd parties, including bot developers. Having developed Discord bots, I can tell you that you can get pretty unrestricted access (with the server owners cooperation) until you have been added to a bunch of servers (at which point you need Discord approval to get things like message content)
12 to 15 months is the standard schedule, but if you are concerned about being in a measles hotspot, talk to your pediatrician about an earlier vaccination. The current CDC guidance is for infants between 6 and 11 months to get one dose of the vaccine before international travel [0]. Assuming the mother was vaccinated, young babies will inherit the immunity from her for the first few months of their life.
[0] This is in addition to the standard 2 dose vaccine schedule. So such children will end up with 3 doses instead of the normal 2.