If I am working for an enterprise(new start-up) we predicted that we will be having a custimer traffic of around 10,000/day.Our start up is a quick commerce website like zepto/blinkit.

As I am new to the business and don't have much capital to invest.What would be the cost effective AWS EC2 instance service that I can opt for my business

On-demand instances would be the cost-effective option, since it is reliable, has no upfront payment, and can be scaled according to your traffic needs later.
Also using multiple servers located in different availability zones within the same region can ensure uninterrupted operation even if some complications arise in one of the AZ's.
As, you later learn workload patterns, the server instance types and pricing models can be optimized later.

Instead of IIS is there any other third web server software that can be integrated as well and also available as well?

Yes, there are many third party webserver softwares that can be installed manually in the cloud. Some examples are Nginx, Apache Tomcat, Apache HTTP Server, etc.

Instead of IIS is there any other third web server software that can be integrated as well and also available as well?

If I am working for an enterprise(new start-up) we predicted that we will be having a custimer traffic of around 10,000/day.Our start up is a quick commerce website like zepto/blinkit.

As I am new to the business and don't have much capital to invest.What would be the cost effective AWS EC2 instance service that I can opt for my business

Inwhat scenarios I have to go for SHared INstance vs Dedicated Instance vs Dedicated hosts?