MitzeeV1

You can run both at the same time with little issues provided keymaps don't overlap. I've ran both before without issue, however I'd reinforce what is said above and remove Arrest Manager for now as Albo isn't reguarly updating it. There's another mod that adds more police stations and jails if you're using Arrest Manager for that aspect.

If you use LML or OpenIV, there is no need to be worried about overwriting stuff in the game, as the files are loaded seperately. Most of the mods on this site (and mods in general) come with a readme (an instruction for how to install the mod downloaded) - Part of modding is learning how to do the basics yourself, it may seem daunting at first but when you get going with the game modding, it really isn't too much to it. 
 
In my opinion, it's much better to ask if you're stuck on a specific mod which you are trying to install. As for mods to install, look to our downloads section, see which mods are highly rated or looks good to you. There sadly is no one-size fits all. 

Basically, it's saying that you shouldn't be using Arrest Manager and StopThePed together, as some (if not all) of AM's functions are also handled by STP.
 
My recommended course of action for resolving this particular problem would be to uninstall Arrest Manager, as it is not actively maintained (whereas Beijojo does still maintain StopThePed).

No. But YouTubers have a magic tool called "editing" at their disposal. Probably not showing all their crashes 🙂