Hi,
I have carefully read through your project description. Here is my thought:
1. this project consisting of web part(front-end, admin, backend control logic), db, task queue, backend services(your code to trading server)
2. cloud service choices: google app engine/cloud engine, amazon cloud service(AWS), windows azure are all ok. which one is good for you depends on your scalability/availability requirements, for example if you expect a huge number of simultanious user requests on expensive computation load. but I prefer google app engine/cloud engine because it is PaaS without developer worrying about scalability/availability.
3. i propose the following tech stack:
web backend: python/django/google appengine
web frontend: jquery/bootstrap/reactjs/angularjs
db: either google datastore, mongodb, , cassandra, or mysql/postgresql(support for json document store)
task queue: either google appengine taskqueue or zeromq or activemq
log event streaming: kafka
I am senior python devleoper with more than 10 years experience. pls reply for further discussion, milestones etc.