jon

This section, Using a pre-existing subdirectory install, will get you #2:
https://codex.wordpress.org/Giving_WordPress_Its_Own_Directory#Using_a_pre-existing_subdirectory_install
Especially note the sentence “If you already have content in your site, see when your domain name or URLs change for how to deal with references to the old URL that will remain in the database.”

Creating a page called 2016, and replicating your home page there, will get you #1.

Only potential problem: previous bookmarks made by visitors will no longer work.

You are much more likely to get an answer if you post here:
https://wordpress.org/support/theme/novellite

P.S. – that Google search might be better as shown below:
WordPress "An internal server error occurred, please try again later"

Multisite WordPress is meant, out of the box (without plugins), to run in either subdirectories or subdomains. Pick subdomains when you are asked during the install.

The other step is on the Hosting side where you need to set up Wildcard Subdomains or something like that (Hosts call them different names). The concept is to allow WordPress to dynamically create subdomains without any additional human intervention by you or your Host’s support folks.

If it were me, the first thing I would do is build a test Multisite WordPress on your new hosting, and get used to everything. Then build a real one from scratch later, using the test one as a sandbox to play in, and learn, then to delete when done. You might not even have to delete it if you use this approach (i.e. – put the Test and Prod installs in separate subdirectories):
https://codex.wordpress.org/Giving_WordPress_Its_Own_Directory#Using_a_pre-existing_subdirectory_install

My experience with random 500 Internal Server Error is not recent, but I noted in the section in the Codex on the subject:
http://codex.wordpress.org/Common_WordPress_Errors#Internal_Server_Error
that increasing PHP Memory is suggested.

Which reminds me about how many issues I went through on a VPS when it ran out of RAM during periods of high traffic.

My original 500 errors though were caused by my web host’s workload management software. It would kill any processes using any processor time, with a 500 error, whenever it was running out of RAM for the entire shared hosting web server.

My Best Advice depends on whether or not your site is “static” or “dynamic”, in the sense of: could you ensure that the content does not change for 2 weeks?

For a Static site that could go unchanged for 2 weeks, the easiest way would be to migrate and convert to multisite as a single step, from the old host (multiple single sites) to the new host (one multi-site).

For a Dynamic site, where content changes, especially if you get a lot of input from various visitors and users, I would recommend doing the conversion to multi-site on the old hosting company where you are “at home”, as in more familiar with how to do things, and less likely to run into errors. For example, this would mean only one database to create when you move to the new hosting.

See the section “Using a pre-existing subdirectory install”:
https://codex.wordpress.org/Giving_WordPress_Its_Own_Directory#Using_a_pre-existing_subdirectory_install

I have used that approach, as opposed to moving everything to the root directory of the domain, for at least 7 years now, and been very happy with how uncluttered the root remains.