Issues with .htaccess

Hi.
I've never really gotten the hang of .htaccess, and right now I'm a bit stumped
I had a working version, but after upgrading the hosting environment, it broke (maybe in part because of changes in the code as well).
However, right now, I have a semi-working .htaccess, but a couple issues are still present.
Here's the current .htaccess:

#Gzip
<ifmodule mod_deflate.c>
SetOutputFilter DEFLATE
</ifmodule>
#End Gzip

Options +FollowSymLinks
Options -Indexes

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule (css|script|uploads|webgfx|timesheet|translations|reports)/(.+)$ $1/$2 [N,QSA,L]
RewriteRule ^(.*shiftlistreport)|^(.*skiftlisteoversikt)$ index.php?page=reports&subpage=$1 [L,QSA]
RewriteRule ^(.*skiftlisteoversikt)$ index.php?page=reports&subpage=shiftlistreport [L,QSA]
RewriteRule ^(.*)$ index.php?page=$1 [L,QSA]

ErrorDocument 404 /index.php?page=404

<IfModule mod_expires.c>
# Enable expirations
ExpiresActive On
# Default directive
ExpiresDefault "access plus 1 month"
# My favicon
ExpiresByType image/x-icon "access plus 5 years"
# Images
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpg "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
# CSS
ExpiresByType text/css "access 1 month"
# Javascript
ExpiresByType application/javascript "access plus 1 year"
</IfModule>

Code (markup):

This doesn't work (it works for redirecting and stuff, but it delivers an error on the page, and CSS and JS isn't loaded correctly.

If I change around the last RewriteRule a bit, so it looks like this:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?page=$1 [L,QSA]
RewriteRule (css|script|uploads|webgfx|timesheet|translations|reports)/(.+)$ $1/$2 [N,QSA,L]
RewriteRule ^(.*shiftlistreport)|^(.*skiftlisteoversikt)$ index.php?page=reports&subpage=$1 [L,QSA]
RewriteRule ^(.*skiftlisteoversikt)$ index.php?page=reports&subpage=shiftlistreport [L,QSA]

Code (markup):

it works, but the final redirects doesn't trigger at all.

Could anyone tell me how I can achieve the functionality I need?
Ie, I want "pretty urls" domain.com/something redirects to domain.com/index.php?page=something, and I want specific trigger-words to redirect further down the tree domain.com/shiftlistreport redirects to domain.com/index.php?page=reports&sub_page=shiftlistreport
All the while while keeping CSS and scripts and such working, of course. Doesn't really seem to difficult, but I'm probably trying to do this the wrong way