This is a good summary, but there are some things worth adding.
1: Since you stopped watching at Season 2, it should be noted that the later seasons focused greatly on the plot point that not all monsters are evil and some of them are just victims of poor treatment by mewmans, with the heroes' main goal being the mending of mewman/monster relations. Their handling of this plot was distinctly lacking, with several people on the mewmans' side (particularly the Magic High Commission) being portrayed as gratuitously racist and dishonest to the point of being out-of-character.
2: Magic in SVtFoE is so powerful that, even with the Solarian Warriors' defensive strength, there are numerous ways they could have been stopped without destroying magic altogether, using other spells and powers we already know about. Only a few of these were brought up in-show, and as soon as Star decided to destroy magic, everyone went with her plan, even the people who were made of magic and knew they would die as a result.
3: Merging the dimensions wasn't part of Star's plan. She was prepared to be separated from Marco forever as a consequence of destroying the portals between their worlds (in fact, this is the main thing she thought of as "the cost of her plan", not the lives she was ending), but Earth and Mewni suddenly and unexpectedly merged together at the end instead.
4: The aforementioned merging of dimensions, and Star reuniting with Marco, was the final scene of the final episode. Their two worlds are now one world, monsters and mewmans are on earth, helicopters are flying through cloud cities, humans are being driven from their homes by giant spiders, the end. We don't know how any events progress from there, because the show pretty much ended during the next season's prologue.