Just got Arma 3 last night. I was also looking at the Vietnam SOG Prairie Fire DLC too. Let put a few dozen hours in on ARMA 3 to see if it will be worth it.
SOG dlc plays different than the base game. Combat tend to be more intense, often close and personal. If you are going multiplayer i recommend BadCompany RHS invade & Annex if u are having the base game alone. Get the mods the server requires, it only enhances the experience. Yes, at some point in the future i would recommend u get all the mods too. Skip Western Sahara, CSLA Iron Curtain, Global mobilization and contact as those are pretty much campaigns and their assets are never seen used on multiplayer servers. The campaigns just bores me to death. Still can't be bothered to finish it. The firefights are just not as intense as in multiplayer if u seek to experience fear and panic. If u are too lazy for mods but want to see heavy intense fights, try 55th Delta#1/Invade & Annex.
if u are looking for absolute total realism & immersion, i suggest 7Cav servers. The clan focuses on combat realism. They provide 'professional insight' in their trainings which often takes weeks to months if u join the clan. Alot of NATO vets there. I joined, took up the trainings, graduated and quit the clan. They teach combat manuever, CQB and other proficiency trainings, those things they teach in the military. yeah, their servers are heavily modded. U can have a look see at their public server; -7cav-ArmaTacticalRealism, which is heavily modded.
Be warned that the engine is very old and physics in arma is clunky. it is something u would grow very used to and miss if it is gone one day or hate it so much right away u decided u wont play anymore. Oh one more thing, COD and Counter Strike fans will hate this as it is no where as arcady and make u cry.
If you are getting SOG, let me warn u that everybody bangs Yen in Saigon.
I hope one day someone would create a hentai game based on Yen in Saigon. lol. Put that on Steam and am sure SOG Arma fans would want to try it. She sounds like she is the only female in Veitnam anyway, always heard from dialogues from injured soldiers, never seen. Hearing her name mentioned from the lips of injured soldiers seemed to be the only solace when pinned under fire in the darkness for 4 hrs in the jungles of Vietnam. 40 of us would go into the jungles to search and destroy, often only 2 would come out unscratched, wishing how nice it would be just to have a cold beer in the company of Yen in Saigon.
i hope u have settled down and what not, i got so addicted that i think Arma > having a gf. LOL. Yes i admit that i am a legit Arma fanboy.
hope to bump into u sometime. my handle is
snekfud hayashi in the game. yeah i am snake food in the jungles of nam.
Cheers!