Hello hinewwiner,
Looking at your design, I have the following suggestions:
1) As PhillipDAth write use the vMX100 in the AWS. You will ned to pay for the license, of course, but also for the server itself. You can take a look at this document. It explains in detail what you need:
https://documentation.meraki.com/MX-Z/Installation_Guides/vMX100_Setup_Guide_for_Amazon_AWS
2) You might consider using the MX65 (Not W). The MX65 has 8 regular Ethernet switch ports and two additional PoE ports for external AP's. One AP would be more than enough for 15 people, unless they are placed on different floors ;-). MR42 is a nice all-round AP.
Using the switch ports on the MX65 together with the MR42, will enable you to use the EAP-TLS or PEAP fully. This is not possible with the build-in AP in the MX64/65. Also it will be somewhat easier for you to configure guest access. I know that Meraki together with Cisco ISe, has a lot of functionality. Take a look at this document: https://communities.cisco.com/docs/DOC-68192. You can download the ISE as a VM-image and try it for 90 days.
3) The traffic will flow to the HUB, in this case the MX84, and then further on to the AWS. So the MX84 will be single point of failure, unless you configure two hubs: the MX84 and the vMX100. Add them in the list on the spokes, with the MX84 as the first one. If this one fails, the spokes will connect to the vMX100. Just a suggestion ;-).
4) Make sure you do a proper site survey when installing the AP's. This will ensure you have a good user experience, when the network goes live. Nothing more cumbersome, than users complaining all the time ;-). Also, if the environment is dense, in terms of your own AP's and neighbour AP's, or you live close to the harbour/airport, you might want to use smaller channels 20/40MHz and disable DFS. Configure band-steering and disable 802.11b devices. This is also not possible in the 64/65W
5) The client-VPN should work just fine. I think if you use the default Meraki authentication, it is PEAP-MSCHAPv2, but I am not sure. It is if you use the default Meraki authentication together with the MR. I have heard that EAP-TLS is supported with the client-VPN, but this somebody else have to verify. Again EAP-TLS is supported if you use it together with the MR.
HTH
-kruse