It would seem to me that - all these early tries for activity aside - Black can play for a comfortable Hedgehog-type position in which White will not benefit from having played f3 before it was necessary, nor from the bishop's delayed development at f1.

5. f3 e6 6. c4 Be7 7. Nc3 0-0 8. Be3 Nbd7 etc.

Black may even get a better position than in normal Hedgehogs here the knight often goes Nc6-e5-d7.

Well, on 7...Be6, White often ends up with a pretty cool game too with the (forced?) variation :
8. Bxf6 gxf6
9. exd5 and now :

* 9...Qxd5 10. Qxd5 Bxd5 11. Nc3 Bb4 ( Be6 12. 0-0-0 ) 12. 0-0-0 +/= I think
* 9...Bxd5 10. Nc3 Bb4 11. Qd3 with a powerful 0-0-0 coming

My only problem is when a closed position, as in my #1 post, comes up and I'm like " Hmmmm, and now what. "
Sometimes I go for h4-g4, and let's see what happens, but I can' t really call that a plan... 

I hope I'll find some answers in the book you talked about ! 

Yeah, I'm surprised, I've never played against 3...Nf6, so I'll look into 4. dxc5.

Concerning 6. Nb3 d5, I always thought it was better to play for White after :
7. Bg5 d4
8. c3 Nc6
9. Bb5 dxc3
10. Qxd8+ Kxd8
11. Nc3
Mmmh, or 9...Qb6 10. Bxc6+ bxc6 11. cxd4 Ba6 which looks pretty good for Black actually 

I'll also look in 5. Bb5+, thank you very much !

According to S. Kasparov White gets a bit of an edge after taking at c5 and this indeed looks at least a bit irritating for Black from a first glance.

Woh !
Exactly what I was looking for, Thank you !

Hi everybody !

Against the Najdorf, I play against stronger players :
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. f3 !?

With that move, I can play a Maróczy Bind and develop my pieces naturally. 
I'd like to know what are the main plans on each side (OK, it's boring, but there must be ideas !  )
The position often goes :
5...e5 ( better be played right now if you plan to do it, because after c4, the retreat of the Knight will be better in c2)
6. Cb3 Be6
7. c4 Be7
etc.
White will play Be3 - Qd2 - Nc3 (or a3 if c4 is in danger) - Be2 - 0-0 - Rc1 - Rd1 for example.

Nothing happens but it's solid so what would be the Black plans to try to play for the advantage here, and what White could do to play for an advantage ( except by changing their opening  )

Thank you for your answers, 

MrPatate