You will love guided math. Our school piloted GoMath, but didn't end up purchasing

A lot of other teachers do away with a big whole group chunk when they adopt guided math. I choose not to. I still do a half hour of whole group math most days. This works best for me and when I'm working with kids in small group they are already have a foundation for the skills we will be practicing. It also ensures that every kid accesses the core content. Like you, I have so many kids with varying needs at varying levels. The small groups allow us to work on the skills that they're missing and the new skills. If I didn't do that whole group math time I'm not sure I would be able to fit it in.

So, each day I do 45 minutes of guided math and 30 minutes of whole group, but I think you have to find what works for you in all of it.