I hope your worries are unfounded Stan because I have signed up as a volunteer for the trial (on the long list...not yet selected).
The control arm is a licensed vaccine (MenACWY) I am believing that the CoVid vaccine is built on the same framework and so will be partially safety checked, but you are right, and you can never be sure.
You ask "will all the drug interactions be known", obviously not, and they never will have been, as new drugs and new drug combinations are being produced all the time.
However I am really not sure who is saying September for mass vaccinations, as the trial part I may/maynot be on will not finish until next Spring at the earliest. As said to KooPee since the people in the trial are simply being released into the community to get "infected", it is going to take a long time for the results to come through, especially if the virus is mostly contained and there is no 2nd wave.