Ok, first, for mean sims, remember that personality points are on a slider. So if sims have a lot of Active points, they're Active, but if they don't have any, they're Lazy. Same goes for Grouchy/Nice. If they have a lot of points, the sim is Nice, if not, they're Grouchy or mean. So if you want more mean sims around, don't give your sims too many Nice points--3 or less points is good. If a sim is in the 4-6 range, you may see some mean behavior, but probably not very often. If they have as many as 7-10, you probably won't ever see them be mean, unless they're cheated on or something, and made enemies, or are furious, with someone. With three or less points sims are quick to Argue instead of Chat and are less likely to accept Appreciate interactions unless they know a sim well. You might also see them prank people more often, and they are notorious for cheating at chess, and throwing the ball too hard when playing catch. And, yes, they do start fights. You can read the wiki for more info on personality:
https://sims.fandom.com/wiki/Personality
Also remember that sims can get upset by many things and relationships can go bad just through failed interactions--you don't always need a mean sim to start a fight. So sometimes sims will talk, but disagree and even up with some negative points. Or maybe, like I said above, someone tries to tell a Dirty Joke or Admire another, and that sim doesn't like it--again, that will lead to negative relationship points. Once sims have a few negative relationship points, they'll start to pick on each other and fight all on their own. It'll probably start with some poking or insults and slowly escalate to fights. Sims also get mad if they catch someone cheating on them and in a regular game, that's pretty easy--sims with a crush or higher will get jealous and upset if they see the person they have a crush on perform a romantic interaction with another sim. Even if that person they have a crush on doesn't like them back. And this is why you might see a lot of fights and drama with ACR.
About ACR, I wouldn't say it's dangerous--at least not in a game breaking way. It's a safe and well-tested mod and I've personally used it for years. I would recommend it for simmers looking to increase autonomous romance--I just like to let others know that it's a big mod. Or in other words, you'll see a lot of changes, and you'll have to check the mods you install (or have previously installed) for conflicts. You should be doing that for all mods you install, but again, I mention it for simmers new to downloading. Also, while I do like ACR, I find it best when you customize its settings to your personal gameplay style. That's one of the mod's strengths--it does let you customize a lot--but at the same time it can be overwhelming for someone new to it, especially if you only want one or two features. So yeah, try increasing your sims' romantic interactions without mods first, but don't be scared to try it. And remember you can ask about it here on MTS, too. There have been plenty of discussions about ACR before, so you can do a search on the TS2 forum here to read more about it if you're curious.
Otherwise, if you don't see your sims falling in love very often, try setting their gender preference. Once sims' gender preferences are set, they are more likely to make romantic interactions. If not set, sims tend not to do romantic interactions. ACR does allow you to set preferences, and that's one of the core features of how it works, but you can also do it through the Sim Blender. If you don't already have that, I recommend this update by William/Whoward69
here; otherwise you can find the original in the
Simbology archive. It is also by
Twojeffs and, if you look under Twojeffs' mod section, you can find a copy for your latest EP.
With either mod (via ACR or Sim Blender), you can set the level of gender preferences you want to see in the hood. In other words, what percent you want to be straight, bi, or gay. Once you select that, you run the randomizer (don't worry, you can choose if you want sims with preferences already set to keep their preferences). In that process, pretty much all the eligible sims in your hood--playable and townie--will be given a gender preference. So, when you see them out and about around town, the game's chemistry system should kick in, allowing them to find other sims attractive. And, once they meet someone they like, they'll start doing romantic interactions all on their own and forming relationships.
Finally, one last tip is to visit community lots often and make sure you have a bunch of visitors, if your computer can handle it. If you stay on the home lot, you probably won't see sims form too many relationships by themselves, especially if you are the type of player to control your sims often. You'll need to give sims some time to act on Free Will, and one of the best ways to do that is by visiting community lots. When you visit, your other playables and townies will show up on the lot, and while you are busy with your current household, they'll entertain themselves. They'll play games and do the activities you have available on the lot, but they'll also form relationships while they hang out and talk, too. Sometimes that leads to romance, other times it leads to fights.
So try visiting community lots often and see how many people show up. If it's only 5 or 6, maybe increase that, if you're computer can handle it. You can do that by adding a line in your userStartup.cheat file; add "intProp maxNumOfVisitingSims XX" to your file; replace "XX" with the number you want. Maybe start with 15; I wouldn't do higher than 30, especially if your community lots are small. The number includes the npcs on the lot, by the way, so 15-20 will let you have a few npcs on the lot and you'll still get about 10 sims to show up.
Just doing those two things--making sure more people are around and have Free Will to interact, and then setting sims' gender preferences--should help you see sims by more dynamic and start fights and romances.