Short answer: yes, you can go ahead and create those volumes because the creation of volumes on the XtremIO array is not going to consume any physical capacity in the array (you have 3.088TB of free flash capacity).  However, you need to have an understanding of the dedupe ratio, compression ratio, thin provisioning and other space savings that you can expect on the new volumes that you are going to create. These savings would depend on the data that you are going to store on those new volumes - and thats where you can ask you EMC account team to run the MiTrend tool and tell you what those savings would be. In other words, your new volumes can be 8TB in size, but how much data are you going to store in those volumes, how much would that deduplicate and compress, etc.
How many volumes can be created in 10TB single brick XtremIO out of 7.58TB physical space?
How many volumes can be created in 10TB single brick XtremIO out of 7.58TB 
physical space?