I’m Completely new to Discourse. You can say, I’m a virgin 
at Discourse.
I’m Expecting User interactions
Max 500 Online Concurrent Users Reading Posts
Max 50 Posts/Replay Per Minute
Every Topic Contains 2Images(2MB) Average
Suggest Hosting Plans? Suitable Hardware Requirements(RAM/Processor/SSD)?
While this may be wildly inaccurate depending upon the user behavior but in my understanding, Going a conservative route of 4 CPU Cores and at least 8 GB of RAM coupled with SSD storage (whatever you need depending upon your content requirement + 25%) should give you enough headroom.
Try to use recent version of CPU to benefit from their performance.
Thanks @itsbhanusharma
have you hosted any forum?
if yes
then please share your current user interactions & Hosting Plan with Hardware. & also Forum Link
I don’t have any hosted forum myself but I do have many client forums as case studies:
where you hosted this suggest me.
I am starting a forum for social work in India. Now I want to test this with my City Aurangabad.
If I successfully tested this concept then I Want to promote it to all Over India.
I want to start Different Discourse for every City with Subdomain Example: Aurangabad.Example.com, Delhi.Example.com - its just example I have not selected domain name yet.
I’d suggest hosting with Digitalocean (They have a DC location in Bengaluru so good latency across India)
About your plan, I’d suggest go with a rather powerful server and set up discourse multisite to make your life easier.
And I can get involved in it for the development phase since this is a project based in India.
What it means?
I want to set up different discourse for every city because it will need local moderators.
because I want to show city-wise forum to user.
Yes
I am working on this concept development from 6 Month. but i have wasted so much time to thinking it on android. Now i decided website based system will work well because user are lazy to install new apps. Website is easy to use specially Discourse.
I am using similar Discourse forum from 2-3 years.
please give me links of these 3 forums. to check there traffic interactions
Can’t disclose without client consent. Against business policies.
How sure are you will see this kind of activity from day 1? Where are you getting the figures from? Are you migrating an existing forum?
Most hosts offer very scalable solutions. Start with the best you can budget for with a host that has scalability both ways. One thing is that discourse values fast CPU over a group of slower ones.
With images it might be best to consider a “cloud” storage/delivery service like Amazon S3 which is supported by Discourse. This will help with hosting costs, efficiency and visitor experience by offloading image duties to Amazon’s infrastructure.
Multisite could be challenging from a technical and community perspective. Personally I would engage a developer/dev ops person of you choose to go that route. Even if you are capable of the dev ops yourself, it’s probably not the best use of your time.
Otherwise you could setup categories for cities as you roll them out and set the subdomain to redirect to the URL of that category.
You don’t deploy anticipating this load on day one.
Start small and scale up, DigitalOcean will let you do this.
This is just Predictions because i want to calculate expenses. Because this forum for social work.
No i’m not migrating
I think it will not work for me. because I have to set categories to every city.
A separate Discourse instance for each city is likely to become an administration nightmare which is why I’d have look at using a category for each city.
If you use categories then you can have specific “moderators” for each category:
This sort of per city/state structure for a country has been discussed before so you should find some useful info: