Sickening offensive as the L7 talent seems like a nice debuff to ensure that the target of your natural attack blender, assuming they're still up, is at penalties when they return fire. It seems like it'd look right on a horrible ratling ripping into an enemt IMO. I'd probably take extra investigator talent and grab one of the skill talents at level 7 too.
Combat Inspiration is the talent for level 9. Lunge is a feat to help keep you alive then.
On the subject of dipping WHW - I wouldn't. You've got enough scaling based on investigator level that a near-dead level for one extra attack sounds like a poor bargain.
I would consider Sharptooth from the Monster Codex as your 5th or 7th level feat. That will give you claw/claw/bite all as primary attacks. Throw in a tailblade as a secondary attack and you will have four natural attacks right away when you get Studied Combat.
I would wait until later for Piranha Strike. You can afford the penalties better once Studied Combat starts to kick in.
Also the Dirty Tactics Toolbox has a feat called Scurrying Swarmer that sounds amazing for Ratfolk. It comes out Sep. 2. It sounds like some teamwork feats would go great with this one.
