Create an offline repo of an unbuntu release, Linux Mint 19.2 (not 19.3)

I've been for weeks now tried to rsync all files from local servers close to me so I can create my own local/offline repo for this but as it's larger than 120G(the SSD maxed out) it must be lots of 'crap' in there so this is why I ask. It's Linux Mint 19.2 and I guess you have the knowledge of the file system of all the files for this; installation, updates, upgrades etc. I can't understand this as I come from CentOS/RH for my server where they had one directory called something like 'everything' and this had absolutely every file including all updates that was made during it's lifetime. LM(Linux Mint) 19.2 will go EOL in the later part of April but I NEED!!! this as this is the only distro I've found that has a kernel LESS than 4.16, it is 4.15 and it seems to work. No!!! I can't get a newer driver as the hardware is old. In kernel 4.17 the old scsi initialization model are removed from the kernel source thus making this driver not working. I got a big RAID5 system with data I need to access thus my question here. How do I create my own private/offline version for Linux Mint 19.2? I've been trying don't know how many different versions that won't work. I tried something called, apt-mirror but that seems to be obsolete and won't work. I even tried to read that code and I can't understand how this filesystem is setup. I need this so I have more time to either get newer hardware or to use software RAID but this need money to get new disks and that costs a lot so it will take a lot of time to get more than the end of April. I can't use a 'clone' of the system as I can't say how long the hardware will work and also the perhaps programs I need to add later on.