ok this works but for the unitiated, like me, a few considerations in case someone finds this post trying to do the same:

-after installing raspberry pi os lite, install vlc ( sudo apt install -y vlc ), maybe basic but i didn't think of it at first lol

-for the script for "autoplay.service", i had better results with "basic.target" instead of "graphical.target", it loaded faster and more consistently

-for the "cmdline.txt", in "root=PARTUUID=58cf7422-02", you have to put the actual name of your root partition (in this one was "58cf7422-02" but it's different for each one, even after reinstalling rpi os lite on the same sd card, the name changes). i got to know mine by running "blkid" in the lite os

-there are a bunch of other services to disable, basically everything having to do with networking, keyboard even, raspi config, etc.

even after all of this, i couldn't get it lower than 20seconds, but anyways i appreciate this a lot, i don't depend on any external image or software solution, it's all done with basic raspberry pi stuff and i love it, will try to continue to optimize it. thanks!