what percentage of income does one have to give to be in the top 1% in this category of people between those who regularly support charities?

The earlier EA Survey Donation post (and linked notebook/Bookdown chapter on this) may be helpful. 

But I'm not sure which base group you are considering, or what measure you are considering

Base group: All people who identify as EAs, all US Americans, all people in the world, all people in the world with income above some value?

Metric: Top 1% in terms of absolute amounts given or in terms of share of income given? 

I think you might be able tease out the answer to some of your questions from [this paper](https://www.semanticscholar.org/paper/The-Evolving-Distribution-of-Giving-in-the-United-Duquette/48b092a6436e213b45d86e090cce508ac16ab77d). Sorry I don't have the data/numbers to hand, I've worked on this before.