[What goes well with Thugs?]

I prefer Poison because of the Bruiser + Noxious Gas combo.

[What goes well with Poison]

I ran Thugs/Poison before the shutdown and can vouch for it. So much fun. Buffed up bruiser, debuffed enemies, and gangwar. Just good times.

[Fire/Fire Sentinel]

Having fun with Assault Rifles/Fire.

 

I think the point of Sentinels is trading in some range and damage for survivability.  I think the coolest things about /fire on Sentinel is Molten Embrace to add to your primary's damage, Rise of the Phoenix to prevent squad wipes, and Consume to keep your endurance topped off.