Well, fwiw, the inventor of the mRNA vaccine idea, Ingmar Hoerr, thinks side effects are very unlikely, since the mRNA molecules dissolve after a few days. He has been working on this for 20 years, with no serious side effects ever observed.
100% of the 100ug treatment group had at least one symptom, 80% of those classified as moderate. The vaccine is going to make you feel sick for a little while.
But I think SARS died out before the vaccine was ready/needed.
While we cannot totally disregard ADE, I assume we should have seen it by now (and the Oxford trial was stopped exactly because they thought they might have observed something like it). Whether it appears again on a population scale level, nobody knows.