First you can not use "redirect" in your hosting server because this modify the URL.
You must either define an alias or create a domain (or subdomain) that can share the same directory than your master website (or the deploy directory)
In your post, you don't mention which video (number) that you have applied.
Did you use {site_url}/multisites/{site_id} that is a subdirectory and avoid to setup the hosting server or did you try setup a subdomain ?
If you have defined a subdomain, you can check that you have configured your hosting server correctly with the "hello world" procedure.
This will help you check that you can access the directory that you have specified in your hosting server (not in JMS).
Once you are able to access and execute the "hello world" in this directory then you can try deploy the slave site in this directory.
If you still have "internal server error", this is perhaps related to the owner of the files that is used (or they does not have execute permission or something like that that you can compare with the hello world working).
Your symptom seem to be related to a permission somewher.
If you want that we have a look on your server, this is possible with our billable support that you can order at
www.jms2win.com/download?page=shop.produ...35&category_id=1