OK, it's coming to the point where I'm not enjoying the game because I find it way too easy. It's a joke how much loot there is and how easy it is to get stuff that makes you OP. Are the any mods or suggestions to make the game more tactical and challenging? Like, a lot? I've been playing on Hard without companions. I've been playing OWB and not really getting much out of it because of how short the battles are compared to all the looting and inventory management. Like, it takes me 2 minutes to clear a building and then 20 to get everything I want and stockpile it with the rest. A mod that makes caps and loot much scarcer would be great. If it's not DLC-compatible, so be it.

Very Hard hardcoe Dead is Dead playthroughs are always challenging, especially with Dead Money and Lonesome Road.

As for mods you could try Project Nevada. It can make combat more difficult and more tactical.

You could also try a no kill playthrough (dead is dead of course), you'd be surprised how hard it can be to avoid being killed without killing anything yourself in certain situations. Running for your life from Legion assassins is much scarier when you can't even try to fight back.

Project Nevada covers a lot of the bases. There are four modules, but the Rebalance one sounds like the one you want. It allows you to:
-Customize the amount of HP you start with and the amount you get per Endurance point
-^Same with AP and Agility
-^Same with Carry Weight and Strength
-Customize the amount of damage you and enemies take
-Customize the amount of HP enemies have
-Customize the percentage of Experience Points you get
-Customize how rare ammo and food are
-Gives food different classes, a Stale Salisbury Steak is not as good for as a Sealed Salisbury Steak
-Can change the levels you get perks on
-Customize how easy or hard you want sneaking to be
-Customize the height at which a fall will hurt
-Many other things

You can find it http://newvegasnexus.com/downloads/file.php?id=40040 and you should probably move this to the mods section if you wanted to focus on that. I agree with Tycho, a Dead is Dead playthrough on Very Hard and hardcoe with no killing would be an incredible challenge.

Arwen's Realism Tweaks makes combat MUCH more dangerous, reduces loot and quite a bit more. It's very well done, and honestly makes the game immensely harder. It also makes you beg and pray for cover.

I've heard a lot about it, how is it compared to Project Nevada. Does it make all of the changes automatically or does it give you a way to customize it?

It's modular, so you can use the parts you want, and not the parts you don't. It's not really adjustable, though, and is focused heavily on making it more realistic. No modules that add more cyberware, or equipment modules. And the Med-Tec module, while absolutely awesome, is brutal. It forces you to rethink your playstyle, as getting shot or stabbed is suddenly very dangerous. Carry some emergency medical supplies!