Suggestion for software architecture for event management software using modern technology

I have been a .net developer and know asp.net, vb.net, c#, javascript, html, css, sql and some other technologies. I can understand software pattern and practices and have coded some apps using 3 tier architecture.

However, I am in to project management now but want to enhance my skills using some modern tech. I have some introduction about cloud, microservices, AWS, angular etc but do not have much detailed knowledge (like JS, asp.net ,SQL).

I am planning to build an event management system which would basically have an event organizer log in and setup events and then have the end user login using google/facebook and subscribe and purchase for events.

I MUST have the mobile version of this app (ofcourse along with the web version). The project looks very simple and i could easily code this in 2/3 tier with asp.net, SQL and JS but i would want to have application features as below and learn new tech. for myself :

1. no downtime of application (may be i can utilize the cloud but need to know in depth)
2. dynamic scaling of the apps - if a particular event has more selling of tickets or higher volume, i do not want to get additional RAM or space on server. it should auto-scale (i believe AWS/Azure might have something on this but i am not aware).
3. open source is welcome, I know asp.net hosting on IIS on AWS would cost rather than asp.net/nodejs on linux box on AWS, same goes for database.

Please suggest me the rights architecture. I thought of : SQL as DB (open to any other SQL/NoSQL database as well) asp.net core microservices for business rules angular + css + html + android UI + iphone UI as fron tend which would make calls to microservice APIs.

Please Suggest. Thanks