complex .htaccess redirect - apache

Question

"domain.com" is my root domain and I have several other domains linked to it as alias domains - let's call those "domain2.com". They work exactly the same as the root but are used for alternate spelling and .net, .de, etc extensions.
I also have some domains that I bought for friends redirecting to their own webspaces - let's call those "domain3.com".
At last I have a single domain "domain4.com" that is also an alias but should behave differently.
I have listed my requirements here:
domain.com
-> root domain
-> wildcard SSL certificate
-> remove www
-> redirect anything to https://
-> "foo" subdomain is automatically redirected to /.sub-foo/ folder
(server setting that I have no influence in)
-> if possible preserve https://foo.domain.com/ in the address bar instead
of https://domain.com/.sub-foo/
domain2.com
-> alias domain linked to domain.com
-> no SSL certificate
-> redirect everything to domain.com, including Request URI and any subdomains
-> address bar should change to domain.com
domain3.com
-> alias domain linked to domain.com
-> redirect everything to external.domain.com, including Request URI
NOT including any subdomains
-> address bar should change to external.domain.com
domain4.com:
-> alias domain linked to domain.com
-> no SSL certificate
-> remove www
-> remove ANY subdomain used
-> remove ANY request URI used
-> ALWAYS redirect to the domain, no matter what
-> redirect that domain to the folder domain.com/subdir/
EDIT: Okay, after a whole lot of try and error I finally have found a mostly complete solution.
### domain3.com ###
RewriteCond %{HTTP_HOST} ^(.*\.)?domain3\.com$ [NC]
RewriteCond %{REQUEST_URI} ^(\/)(\.sub-.*\/)?(.*)?$ [NC]
RewriteRule ^(.*)$ http://external.domain.com/%3 [L,R]
### domain4.com ###
# check if any subdomain is used and remove it
RewriteCond %{HTTP_HOST} !^domain4\.com$ [NC]
RewriteCond %{HTTP_HOST} ^(.*\.)?domain4\.com$ [NC]
RewriteRule ^(.*)$ http://domain4.com/ [L,R]
# check if redirected subdomain is used and remove it
RewriteCond %{HTTP_HOST} ^domain4\.com$ [NC]
RewriteCond %{REQUEST_URI} ^(\/)(\.sub-.*\/)(.*)?$ [NC]
RewriteRule ^(.*)$ http://domain4.com/ [L,R]
# check if any request is used and remove it
RewriteCond %{HTTP_HOST} ^domain4\.com$ [NC]
RewriteCond %{REQUEST_URI} ^(\/)(.*)$ [NC]
RewriteRule ^(.*)$ http://domain4.com/ [L,R]
# redirect to subdir/ directory
RewriteCond %{HTTP_HOST} ^domain4\.com$ [NC]
RewriteRule !^subdir/ subdir/ [L,NC]
### domain.com ###
# remove www subdomain and redirect to HTTPS
RewriteCond %{HTTP_HOST} !^domain\.com$ [NC]
RewriteCond %{HTTP_HOST} ^(www\.)?domain\.com$ [NC]
RewriteRule ^(.*)$ https://domain.com/$1 [L,R]
# redirect subdomain to https
RewriteCond %{HTTP_HOST} !^domain\.com$ [NC]
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} ^(.*\.)domain\.com$ [NC]
RewriteRule ^(.*)$ https://domain.com/$1 [L,R]
# redirect http to https
RewriteCond %{HTTP_HOST} ^domain\.com$ [NC]
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://domain.com/$1 [L,R]
### domain2.com ###
# remove www subdomain and redirect to HTTPS root domain
RewriteCond %{HTTP_HOST} !^domain2\.com$ [NC]
RewriteCond %{HTTP_HOST} ^(www\.)?domain2\.com$ [NC]
RewriteRule ^(.*)$ https://domain.com/$1 [L,R]
# redirect subdomain to https root domain
RewriteCond %{HTTP_HOST} !^domain2\.com$ [NC]
RewriteCond %{HTTP_HOST} ^(.*\.)domain2\.com$ [NC]
RewriteRule ^(.*)$ https://domain.com/$1 [L,R]
### copy domain2.com code for every other "domain2.com" like domain
### I have this code 6 times in my htaccess
For those who wonder about the 2nd RewriteRule part of the domain2.com - I can't use "https://%1domain.com/$1" which would be the "correct" approach, because my server alters the subdomain to "/.sub-foo/" BEFORE the .htaccess is processed.
The only thing NOT working (and I'm not sure I even will get this to work anyways) is that the address bar displays https://domain.com/.sub-foo/bar.php instead of https://foo.domain.com/bar.php
I'll try and talk to my hoster if he can deactivate the automatic redirect so that I can solve this via .htaccess alone.
If anyone has an idea how to shorten this monster - help would be appreciated.