I'm planning my first character with following stats:
STR 4
PER 5
END 4
CHA 6
INT 10
AGI 5
LCK 6

or should I put STR down to 3 and get END to 5? With weapons handling + 1 str implant I could use weapons with str 6 requirement, but if I take 4 in the beginning I could use weapons with str req of 7. Are there even any str 7 requirement weapons?

If you dont plan on effectively using large weapons str 4 should be okay from what I know. Yes I think there are some weapon that require 7 strength anti-material rifle for example

anti-material rifle is 8 str, and you can still use it with 6 str. You just wont do max dam or accuracy.

Anti-Materiel requires str 8. If I take STR 4, implant and weapons handling I would be able to use STR req 7 weapons. Are there any worthwhile req7 weapons at all? Otherwise I'll just drop str to 3 and put that extra point into charisma or endurance.

You don't get weapons handling til level 16. So even if the build works well you'll have to play through a big part of the game without it.

For the anti materiel rifle you're going to need to be a strong person. You can still be an effective sniper without that gun though.

Indeed. I guess I won't lower STR to 3 then. And with STR 5 (implant included) I can get a few perks like strong back.

Intelligence only gives a half point per level in New Vegas, it gave 1 point per level in fallout 3. New Vegas is balanced for 30 levels instead of 20.

Remember that you can always use a few levels of the Intense Training perk.

I'd honestly drop starting INT to 9 and get the Implant asap in game.I went with an 8 and spent a perk on 1 and the implant.Get the perk for the extra 2 skill points a level...if your gonna go 10 int...go all the way I say.
Yes...17 skill points a level is really,really nice...but not much better than 14-15 I suppose.Given the rarity of permenant enhancements though..