Hardware and performance

You may also consider configuring and supporting the Moodle mobile app. This is because it has a connect and synchronize technology whereby you can still work on things when you don't have a working internet connection.  You need to turn it on in your Moodle and make sure you don't rely on any plugins that do not support the App and don't try to deliver things that Mobile devices tend not to support, e.g. Flash.

I have set up a Raspberry Pi and it was a great way to learn to install an OS,  LAMP stack and Moodle from scratch. It was perfectly functional and with a tiny router powered by a USB Powerbank,  made a portable solution I could just about carry in my pocket. I loved being able to set it up, then wipe it and start all over. I could see it being used where there was no power, no internet but the students had mobile phones.

But a PI is really an under-powered beast with 1 gig of RAM, a not very powerful CPU and uses a SD card for writes which has a limited life. With the number of students, something a bit more powerful would be  required and these days many obsolete and discarded computers would have far better specs. Cheapest solution might even be a laptop with a dud screen.

I think unless extreme portability is essential for a small number of students, a Moopi is not a practical production server.

As for the rural school - my advice is suck it and see. The server is a good start and is what you have. Set it up with a LAMP stack (if you can - Windows is not considered  optimal for Moodle) , install Moodle and get started - perhaps with one course at first. Don't underestimate the time required to create course material and for teachers to become familiar with the system. I think the best way to learn Moodle is from running it.

But I do wonder - when will the students use the system? If it is independent of the internet and based around a server and wifi, how will they access it without being in wifi range?

The original post wanted " correct installation of Moodle platform (to be powerful and well established) on a server that I am currently working with.". That server already has 2GB of Ram - twice that of a Pi - and probably a faster CPU. I am assuming rural does not mean a place without electricity.

My solution (assuming the Win machine is not used for other purposes) would be to install a basic Linux distro and Moodle.  Add a router ( approx the cost of a Pi) connected by a cable and you have a system which could handle many connections.

Maybe you could use a Pi but why buy a new computer when you already have one that can handle the job? Portability was not specified by the original poster. And powerful and well established does not sound like a classroom of students connecting to the wireless output of a battery driven under-powered computer using a SD card for storage.

Two additional drawbacks of the mobile Pi. There is no shutdown switch on a Pi and if you are short of time or careless and you simply cut the power, you may really screw up your databases and Moodle.  You can use a Mobile phone to shutdown but more complexity.  And my own Pi died in a thunder storm - the only electrical thing that died in the house and probably my fault for using a phone charger rather than an approved power supply.