@Nexxus Definitely way more realistic than default IV. If you want IV-stylish handling in V, I'd suggest Classic Handling by Alexander Blade, though I wouldn't play the storyline with it.

Technically and theoretically with the right PC - yes. Though your traffic variety will be messed up because of the memory usage of most of the vehicle mods due to their size.
Biggest problem will be that you won't be able to find much more suitable good quality vehicle mods at some point - especially if you're planning to replace every car with their real life counterpart.
And BTW, with the right commandline it's no problem having a lot of vehicle mods installed in IV

And yep, custom vehicle models can affect the handling. Haven't used any custom vehicle models with Sim-cade handling except for a few vanilla edits but I'd suggest you to simply try it out.
Also, many vehicle mods are coming with their own handling lines anyway. So what you're going to do is installing the handling mod first and then you'll probably end up editing the handling.meta to use the handling lines coming with most of the vehicle mods.

I'm using Sim-cade Handling 2.5 by chang63.
That's the best handling mod I ever came across and I definitely highly recommend it.
Newest Version is 3.x, I'd suggest you to try out which version you like most. 3.x is more realism oriented & based on the real life counterparts of the V cars while 2.x focuses more on game play in general.
Also, I'm currently playing the storyline again, so far had only one issue regarding the Seashark handling with 3.2, which was fixed instantly with the 3.3 update.

What about... telling us what kind of mod you're talking about? Or even better - the name of the mod itself? Or reading the ReadMe which is most likely attached to the mod?
How should we be able to help you if you're not giving us any information?

Also got one or two suggestions:

• Prisoner Transports leaving Bolingbroke
• Traffic Stops - remember the ones seen in Liberty City on Columbus Avenue and on East Borough Bridge?
• way more Taxis arriving/waiting/leaving at Los Santos International - currently, you can only see one or two taxis pulling out of two of the taxi stands

One idea crosses my mind since I saw the first the major construction sites in the GTA universe: 'breathing' construction sides.
Now, I don't want the NPCs to build the High Mile CLub in Downtown LS ... I'm talking about construction sides with some action happening - trucks arriving/leaving the scene, bulldozers roaming around, workers carrying building material or even moving cranes and so on.

@Cass In what way is that possible through vanilla edits? Looks like you're the expert on this

@opc-power Ich hab dir zwei Fragen gestellt - und eine beantwortet.
Und - hast du schon mal versucht, OpenIV neu zu installieren?

Oh, then... I'm sorry. Didn't know that.

@WaZzUp Are you talking about vanilla cars or custom models?
Are you using ELS?
Did you modify carols.ymt or carvariations.meta?
Give us some more input...

@opc-power Echt jetzt? Das ist ein englisches Forum...
Abgesehen davon, bist du sicher, dass du V in den gleichen Pfad wie zuvor installiert hast?
Und was meinst du mit "neuester Version"?
Aber normalerweise arbeitet OpenIV auch mit älteren, ungepatchten Versionen.

That's an english forum...
Apart from that, are your sure your installation path of V is the same as before?
Also, what do you mean by 'newest version'?
However, OpenIV also works with older, not patched game versions.