Server configuration and hosting location for a website with 100,000 visitors daily?

Depends on your server configurations, if you are using a right webserver and do some optimization for your server (especially PHP and database related), you can reduce your server's resource usage. As a startup, I recommend you to use 2 GB RAM VPS to handle it, or if you're not sure enough, you can use 8 GB RAM dedicated server, I prefer in USA, not about speed, but USA servers has a better network quality and lower price.

There is no way to know. Deploy, and measure. Buy servers for a day or two on Amazon AWS, Singapore. Do a load test from other machines in India. See if you can survive, only then take a call on what servers to purchase. You will have to spend money to understand how to spend it efficiently. :) There are things you need to consider: What is the visitor load profile? Do you see 100,000 visitors equally divided through the day or does it follow a bell curve kind of a deal? If so, what is the peak requests per second? You need to support atleast twice that volume. Are you okay with running a bunch of very small servers behind a load-balancer? If your host lets you pay by the hour, say AWS, you could consider running a few micro instances and then adding more close to the crucial load hours everyday. This is hectic, probably open to automation, but may save you a bunch of money. What is the CPU load profile? Do you run some jobs at the end of the day? Would you face more CPU usage at the end of the day? Can you spread out the jobs through out the day to see lesser load at any given time? Could you spread out your jobs to other instances that come to live only when they are required? This is also hectic, but again, saves you a lot of money. There is no perceptible delay if your servers are out of India. It is mostly (please don't kill me here) a function of how you host your static assets. Have a look at a CDN like akamai. Also, as I keep telling everybody I know, https://codeascraft.com/2011/02/15/measure-anything-measure-everything/. This will tell you how you are doing and what you should be doing about it.

100k users under which scenario? How the typical session looks like? If you have 500k pageviews, its 20k pageviews per hour in average, so usually it means 3-6 times more in the peak times. So let's say 120k pageviews per hour as a maximum. It's 33 pageviews per second. Do a benchmark on some development server and start from there. Keep in mind that scaling is not usually just adding RAM and Drives. If you will need a dedicated database (quite likely) benchmark this scenario too. I've seen a project for a very well known brand where they missed to measure the network load to the database servers and their poor design killed the app as soon as about 20 people came to the site.