I'd go dex route* with Weapon Finesse and Agile Amulet of Mighty Fists.
You won't need Amulet of Natural Armor as much as martials since you have Barkskin on your formulae list, and Str-based isn't really a good choice since you're only proficient in Light Armor.
*If you were planning on raising Str. You talked about Power Attack so I assumed that was the case.
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Ability Scores
Your Stat priority should look like this:
Dex>Int>Con>Wis>Str>Cha
Dex is your Attack/Damage/AC/Initiative/Reflex Save, so you will probably want to keep it as high as you can.
Int is for your Extracts, and not much else. You'd want to keep it high enough to get bonus extracts per day, but you won't bother with having high DCs for your extracts since you'll mostly use them to buff yourself.
Con. D8 hit dice in melee? You might have Sneak Attack as a Rogue, but you don't need to die as a Rogue.
Wis. You got weak Will save progression, and going Dex will lower your Wisdom score with 2 when you're using mutagens.
Str. Only good for carrying capacity.
Cha. Nothing. Good for nothing. Dump it.
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Progression
1. Weapon Finesse, Feat
2. Feral Mutagen Discovery
Yeah, not much to say.
3. Feat
4. Tumor Familiar Discovery/Bleeding Attack
Alright, if you take a Tumor Familiar with the protector archetype it can soak half of your damage taken with its Fast Healing 5. In addition to the usual benefits of having a familiar, such as a +2 to Will saves from the Hedgehog familiar.
Bleeding Attack will give you 3 more damage per turn (at level 6) if you hit an enemy with your Sneak Attack. The Bleed damage will not stack with itself.
5. Feat
6. Wings Discovery
Never underestimate the power of flight. Your movement speed is now 60 instead of 30, melee martials can't reach you if you hover 10 ft above ground, and you never have to worry about falling. Don't forget to invest skill ranks into the Fly skill.
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Feats
First of all, Piranha Strike is the Dex-alternative to Power Attack, and will let you keep your Str score below 13. But using PS/PA might actually do more harm then good when you have 3/4 BAB progression and lots of precision damage riding on your attacks. It's better to raise your accuracy as a Vivisectionist.
Extra Discovery is a thing. Maybe you'll take the Discovery you didn't take at level 4, or the Enhance Potion Discovery if you want to make good use of your Alchemical Allocation extracts.
Step Up + Press to the Wall might be your secondary way of dealing Sneak Attack; for when you don't have a flank partner. But if your GM doesn't have much terrain in the fights then the feat will lose much, if not all, of its worth.
Master Alchemist. Do you want to be a real alchemist? This is the feat you want. 10x crafting speed.
Toughness. Can't hurt to have more HP.
Iron Will. Better patch that hole in your defenses.
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And don't worry if you're not qualifying for the feats you want to take at the level you gained the feat. You could just retrain them.
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Another point to consider is if you want to add another archetype to your build.
The Internal Alchemist trades away Throw Anything (which you won't need now that you don't have bombs), Swift Alchemy and Poison Use.
In exchange you get a neat ability to hold your breath for hours at a time, your Poison Resistance will apply to Diseases, and you also get Uncanny Dodge (Real nice for Dex-based builds).
Coup de Grace is a single attack, so you wouldn't hit with all 3 of your natural attacks.
You can however choose which of your natural attacks you use. Either your bite or one of your claws.