So I can CHOOSE 0311,0313,0331,0321,0351, 0352,or 0341 but as a secondary they ASSIGN me to 0314, 0316, 0312, 0317 0323,0324, 0326?
You can choose 03XX. The Corps will choose the primary MOS.

For the others:

Any of the boat Coxswain MOS you need to have a need to go to school i.e. assigned to the designated Boat Company of a MEU, assigned to Recon, Assigned to FAST and some MCSF Co's or RTT's, possibly ANGLICO.

Any of the Recon you must first be an 0321, and go to jump & dive schools.

Scout Sniper you must be accepted to STA platoon and complete the MOS awarding school to become a HOG and rate the MOS.
So they assign me 0311,0313,0331,0321,0351, 0352,or 0341, but I have to take a course for 0314, 0316, 0312, 0317 0323,0324, 0326?
Oh well if you go to BRC. Isn't 0317 a primary course? It's pretty much the same as 0321 'cause you gotta go to school for it.
No it's not the same, schools are different but a 0321 can become an 0317 and vise versa. But you can enlist for 0321 take the 0311 course go to BRC and graduate with a 0321 primary .......you can't do that with 0317.
Enlist as 0321, take basic rifleman course THEN go to BRC and grad with recon... sounds like a good plan. Just so long as I graduate BRC. I wanna get mentally prepared just don't know how.
Mostly it was the personal protection bit.

The whole Protection Detail in Security Forces is like the designation of Antiterrorist in FAST.

There are Marginal Protection Details and they are usually assigned to 8154's on RTT's. But just as FAST really doesn't go out looking for Tango's real world high profile protection details are not going to Security Forces they go to other elements.