So when shoud i install the add ons ? I mean at first i installed them with the game earlier but i decided that if i start the game (level 1) at the verry start havving the weapons from the add on and having stuff will be some kind of cheating. So i uninstaled the game and instaled it again without the add ons. So now im level 11or 12 and my general idea is to get to the Second battle of hoover dam and then install them. What do you think when shoud all the add ons be instaled ? At what time in the game ?

You can just drop the weapons from the add-ons.

By the time you get to the final battle, those weapons (the Courier's Stash items) are not going to be of any use to you except for stuffing into a locker somewhere. They're strictly starter items, and chances are you've probably already outgrown most of them at your current level.

I install the add-ons at the start of a game. For one thing, you'll miss out on the level cap increases and new perks added by the four large DLC if you don't install them. You''ll also not be able to purchase the weapons added by Gun Runners' Arsenal until you install it. If you think the Courier's Stash items are a cheat, just keep what you want and dump the rest into a container someplace (or sell it).

But i reinstaled the game and now i dont have the add ons. and like i said im level 12. If i reach the final battle and then install them is taht ok. Will that increase my level cap or do i have to star the game all over again ?

You'll get the level cap increases (and new perks) when you install Dead Money, Honest Hearts, Old World Blues and Lonesome Road, even if you wait that long. Just make sure you do those DLC before you enter the final battle; the game ends after the battle and you won't be able to go back with that character.

So basicly i shoud make the DLCs right before the final battle and then do the Hoover dam battle ? What if i do the battle and then do the dlcs or that t means that if i finish the main quest then i have to restart the game and do the dlcs ?

You can't do the Hoover Dam battle first - the game is over once you complete that battle, and all you can do is watch the ending slideshow. You'll either have to restart the game with a new character, or make a save before entering the Hoover Dam battle (the game will warn you and make an autosave for you at that point), reload that save and play the DLC and then re-do the Hoover Dam battle after you finish the DLC.

You could always uninstall the add-ons that give you the extra items, and just use the DLCs. That's what I do. The extra items are added in the esps that have "stash" in their names.

Roger. Thanks for the info.