Prepare and enable elasticsearch cluster for Production

By the end of this week I'll be setup ES cluster for GitLab.com. Following work will be done:

Prepare three nodes of DS13 VMs (8 cores, 56GB, 25600 iops for main, but for other attached disks it will be max 5000)
20x1023GB disks, striped LVM (can someone provide estimates here?)
All in one vmnet
Prepare monitoring for elasticsearch cluster - https://gitlab.com/gitlab-com/infrastructure/issues/1292
Improve cookbooks regarding elasticsearch.

Main question for me now is the disk size estimate. So any recommendations on it are welcome.