Add 3 master nodes to our cluster configured only default(master/data...) node

[mgjung02 (Noah Jung)]

Now, we run 6 nodes and all of them has default role (master/data...).
For more efficient cluster environment, we want to change our cluster like below.

• Add 2 master-dedicated node. (new node)

• Change one existed node's role to 'master&voting only&data'.

• Change 5 existed node's role to 'data only'.

  [As-Is]

  Node1 (default), Node2 (default), Node3 (default),
  Node4 (default), Node5 (default), Node6 (default)

  [To-Be]

  Node1 (data), Node2 (data), Node3 (data),
  Node4 (data), Node5 (data), Node6 (master&voting only&data)
  Node7 (master-dedicated, new node)
  Node8 (master-dedicated, new node)

So,

1. Please let me know, if there is any problem with our plan. (run 2 dedicated master node &
   1 voting only node)

2. If our plan has no problem, please share me recommended process and how to do this
   without any downtime.

for reference, we use elasticsearch v7.2
Thanks.