301 redirect have I understood this correct?

I do not know about “Redirect 301”, but here is what I use:

RewriteEngine on
RedirectMatch 301 ^/oldpage$ https://mysite.com/newpage/

I do not think it really matters where a redirect is placed, but I have them near the top:

# BEGIN WordPress
ServerSignature Off
AddHandler application/x-httpd-php54s .php
Options -Indexes
DirectoryIndex index.php index.html /index.php
### added redirects
RewriteEngine on
RedirectMatch 301 ^/oldpage$ https://mysite.com/newpage/
.............

I have never seen “RewriteEngine off” anywhere, but I did find this just a moment ago:
http://www.helicontech.com/isapi_rewrite/doc/RewriteEngine.htm

I would guess it is best to just leave it on unless there is a specific need to turn it off. If it is already on, each new re-encounter of “RewriteEngine on” is simple redundant, but actually turning it off and then back on again would add load to the server.