Okay so I finally want to give Fallout 3 another try. Dropped it after playing it for like 10 hours when it was released.

Now I have a question. I want a charismatic character who can talk himself out of any situation when its possible, also I want to get the most of the story & lore but dont really care a lot about the combat, still I dont want to use the easy setting.

1nd: Is it really true that charisma only influences the barter & speech skill and some perks? So theres basically NO POINT in raising it to 10 (9) at the beginning? Is it also the same case for all the DLCs?

2nd: Which stats else would you recommend for a character like described above, luck? intelligence?

Thanks in advance for any answers

For speech characters, I never put Charisma to 10. I think the points are better used elsewhere. Currently have a speech character with Charisma 5, speech 75, level 14, and nearly every challenge is in the 90% chance of success, with some an outright 100%.
I play with rules in my sig, so you can see the extreme that I go to.

SPECIAL 5,6,5,6,6,5

I didn't add it up lol. But you get my meaning. All the bobbleheads and points really add up fast.
The DLC is integrated throughout the entire game. You can usually come and go as you please, save a couple of places for a short time.

Yes but I heard there also are some special conversation options for characters with a certain high charisma/intelligence/... number

Dont want to miss them, so I am thinking about creating a character with 9 charisma, 9 intelligence but low endurance and strenght at the moment

Well then, I would max out Charisma at 8 then. I choose to avoid adding to Barter at all, cuz, I just do. A high Charisma boosts the barter skill, and I don't want that.
Just slowly add points to your charisma and see what you're willing to give up.

You've got Bobbleheads out there and crazy perks that add points to everything. I don't successfully complete every speech challenge. You won't experience everything the game has to offer in one run. I don't do this, but you could always save before a conversation and reload if you fail.

I personally lower Perception to 1 as you only need it for two perks, Energy Weapons (Which can be avoided by Tagging Energy weapons) and maybe a couple of skill checks that you also could clear with other skills, if you do that though You'll probably want to tag Lockpick as one of your 3 tags. Putting Charisma up to 9 might be a good idea if you don't focus on Intense Training, Charisma in Fallout 3 has a percentage meter that affects Speech checks and it's based on your Charisma rate and not just your Speech skill although the latter too is still useful. Tag Speech, possibly tag a weapon skill so that combat won't be a problem and tag a 3rd skill that you will probably use a lot.

yes I am thinking about something like this at the moment:

strenght 3
perception 1
endurance 3
charisma, intelligence, agility all 9
and luck 6

I plan on using small guns only