Couple problems here Grim...
Pintle Mounted Storm Bolter: Counts as an Extra Storm Bolter and may be used in addition to other weapons the vehicle can fire. So you can't fire it if you can't fire any other weapons. And Ordnance forego EVERY other weapon. So you can only move 6" and fire the Pintle Mounted Storm Bolter, and you can't if you fire Ordnance. That's the way I read it. I checked again in my Codex, and it's a bit hazy about moving full distance, but I know Ordnance forego ALL other weapons. (If you can aim and fire a Storm Bolter while the Battle Cannon kicks, why can't you fire the Heavy Bolter?)
hunter Killers do need line of sight. It's the Tau missiles that don't need line of sight.
As for equipping tanks, it's part effectiveness, part personal taste. I don't like having Sponson Heavy Bolters on my Leman Russ tanks, because you're either firing the battle cannon, or moving and firing the LasCannon, or moving and not firing at all. But for an Exterminator or Conqueror, I definantly put Sponson weapons. For my Gryphon, I'm putting no upgrades whatsoever, and my Manticore is the same way. One of my Chimeras has Smoke Launchers, but I never use them, as I play a defensive game and would prefer to get the shots off over moving. The other Chimera is my Dakka Bunker. Heavy Bolter Turret, Heavy Bolter Hull, Pintle Mounted Storm Bolter.
As for SearchLights... I pay for the two Searchlights in my army EVERY time! Why? Because with Smoke Launchers it balances to 5 points, which is nice, and it's hard to fill 2 points in an Armoured Company ^_^ I laugh every time a Night Fight comes up, because I HAVE Searchlights.