Usman Asar

yes, you can view tutorial HERE, it's based on Server 2012 R2, but will be applicable till 2022 Server edition, procedure remains same.

Heleni, I have a windows server setup tutorial on installing moodle but that does not specifically explains transfer from one server to another, once your new server is setup things wont be difficult. All you have to do is transfer moodle and moodledata folder to new server, re-assign IP's from old to new server and you're done.
If the paths are changed (for example new paths to moodledata folder) then make changes in config.php file.

Kunal, how did you come up to this figure of 4000 concurrent?
Please be clear about the term concurrent, 4000 logged in users are not considered concurrent, for example you clicked to view some resource on moodle, until that request is finised loading from database and moodledata you are considered as concurrent user, so if you're saying there will be 4000 logged in users at one time, then consider 1000 of those to be treated as concurrent.
for RAM, its general consideration of 20 users per GB of RAM, so 64GB should suffice, but this RAM amount should be properly coupled with appropriate CPU and Drive technology with software properly optimized.

Problem is, moodle community doesn't have access to Edumy files to have a look where to change. You'd be in better position to ask the developer to assist you.

December 13 it is to be precise, but in your case upgrading early to 4.0 may put you in trouble regarding additional plug-ins you may be using, as don't expect all additional plug-ins to be upgraded on the same day as 4.0 releases. So if you are using additional plug-ins then I would recommend waiting until all your plug-ins gets updated, else if you aren't, then surely plan your upgrade on weekend after 13th.