Help you require touches two different subjects as you mentioned yourself.
First one is Compression and second is Repacking/Rebuilding of the game files.
When it comes to compression you can find two commonly used ways to do things on this forums.
First way is Inno Setup. Second is FreeArc (along with Precomp an Srep).
For both of them, you can find documentation in form of Sticky topics in this section (first 4-5 topics). There you can find everything you need. If something isn't clear, you can post in respective topics for more detailed help.
Main topics you should check are:
yener90's Inno Project Source Codes
INNO TROUBLESHOOT: Q&A
INNO TROUBLESHOOT - Tutorials
BlackBox Inno Setup
CI (Custom Installer) Tutorial (this one covers both Inno and FreeArc)
altef_4's installer source code
In the end, it all falls down to the fact which method do you prefer and which one do you find easier to "master".
When it comes to Compression Video files, it depends on the game. If the game uses Bink videos, compressing them is pointless as they are compressed as much as it gets (99% of the cases).
Best way for those is to leave them uncompressed because you will lose a lot of time on their compression and difference in size won't matter that much.
The only thing you can do about them is to download Rad Tools (It's free software, you can easily find it on google) and re-compress (rebuild) the videos with 50% (or which ever you prefer) quality. That's the only way to cut their size.
Compression of Audio and Texture files usually goes great with, above mentioned, Inno and FreeArc. You can find more inside the respective topics.
Rebuilding the game files is whole another thing and it depends on the game. While for some games you can easily find tools on google and you can rebuild them easily, there are some games that can't be done this way. Again, it depends on the game and it can't be done every time.