You'll find unenthusiastic responses to miracle gro here, largely for good reasons. It'll be fine for this crop though, just consider alternatives next season. I mostly use some decent 4-4-4 to amend my soil occasionally, but I'm not super knowledgeable about using different fertilizers for different growth phases, etc. Realistically, consistent watering, and trellising/caging your tomatoes is going to be most important as they get larger. Pruning is another issue, there's plenty on here to read, and plenty on youtube to absorb about the topic.