Despite Juniper 'best practice' documentation I would suggest you just move both ICL and ICCP to AE0. This is fully supported and may make you life easier. Then the multi-chassis link protection is associate with this one AE.
As for RSTP, you do know that any form of STP must be disable on any MC-AE - your AE6. Also LACP MUST be enabled on this MC-AE, and therefore also on the edge switch or device. Based upon some of your wording I am guessing your MC-AE is to a device/server vs a switch. In either case, that connection must also support LACP. For this portion of the configuration the LACP system-id and admin key should be the same. Not so sure about any form of STP.
An additional comment is that there are LOTS (way to many) Juniper MC-LAG documents. A google search will probably still return 20+ links. Many of these links are old docs which may very well not contain latest enhancements to MC-LAG and will also have inaccuracies (mistake). I would recommend not using any MC-LAG doc that does not have a publish date in 2016.
Good luck.
As for RSTP, you do know that any form of STP must be disable on any MC-AE - your AE6. Also LACP MUST be enabled on this MC-AE, and therefore also on the edge switch or device. Based upon some of your wording I am guessing your MC-AE is to a device/server vs a switch. In either case, that connection must also support LACP. For this portion of the configuration the LACP system-id and admin key should be the same. Not so sure about any form of STP.
An additional comment is that there are LOTS (way to many) Juniper MC-LAG documents. A google search will probably still return 20+ links. Many of these links are old docs which may very well not contain latest enhancements to MC-LAG and will also have inaccuracies (mistake). I would recommend not using any MC-LAG doc that does not have a publish date in 2016.
Good luck.