I take it he's a natural lycanthrope, not afflicted, right? In either case:
In animal and hybrid form, the lycanthrope's ability scores are the same as the base creature's or the base animal's, whichever ability score is higher.
This means on a score-by-score basis---use the higher of the two Str, the higher of the two Dex, etc.
Since the lycanthrope template is +1 CR, shouldn't the replacement to a level 2 guy be 1st level plus lycanthropy?
Building characters is not my forte (and neither are alchemists), but I'll take a shot at it.
Giant weasels get the grab special ability, so you might want to take Dirty Fighting so that you can then take Improved Grapple and later Greater Grapple. (The non-provoking aspect of Improved Grapple is redundant with grab but the bonuses aren't.)
You could get Improved Unarmed Strike instead, but that's almost certainly less useful for you, unless you plan on taking Feral Combat Training for your bite. Which isn't necessarily a bad idea, as some styles go well with natural attacks, but it does add up to a lot of combat feats for an alchemist.
If the campaign uses the spontaneous alchemy rules from the Alchemy Manual player companion, Instant Alchemy is cool.
Discovery-wise, you might want to rely on Weasel Power for most combat and focus on non-combat and special cases instead of damaging bombs. An exception is Ectoplasmic Bomb, which would let you deal with incorporeals, which can be a serious PITA. Oh, and I like Spontaneous Healing. Nothing jumps out at me as being synergistic with your lycanthropy.
1. Get approval from your GM before making any PC that uses a template. It's easier to ask for permission first before you invest hours into fleshing out the character, as you'll have less attachment to it if the GM says no.
2. Play a natural lycanthrope, not an afflicted one. The CR adjustment is the same, but afflicted lycanthropes are not a good choice for PCs as you can sometimes lose all control of your character when transformed.
3. The lycanthrope template is +1 CR, so that means it counts as one level. Your PC will therefore have 1 less class level than the other PCs, so in a party of second level characters you'll be level 1.
4. For ability scores while in animal/hybrid form, you compare between the base creature and base animal on a score-by-score basis. So you will likely be using your base creature's mental scores, and probably Constitution as well (giant weasel only has 10 there), but Strength and Dexterity will likely be using the base animal's depending on how you allocated your ability scores.
The Aspect of the Beast feat is pretty nifty, both the claws as well as the +2 initiative are decent choices in my opinion. That said, your feral mutagen is strictly better than this feat if you wish to get claw attacks. Beyond that, I don't really play alchemists so I can't comment too much on how to build them, sorry!
Use the triple-threat of melee alchemists:
Vivisectionist archetype to give up those bombs you'll never use for full-progression Sneak Attack, the ability to get Bleeding Attack and/or Crippling Strike, and Regenerate as a 5th-level extract.
Chirurgeon along with it because that's useful and who gives a s&#$ about poison? Also free Skill Focus(Heal) is never bad.
Top it off with Internal Alchemist for Uncanny Dodge and the option of bonus feats instead of Discoveries if you want them. Also gives disease resistance, although that's reduced a little because of Chirurgeon.
You could VMC Rogue to get even more Sneak Attack dice if you wanted, though that may not be the best idea.
Honestly the level adjustment for the lycanthrope template is less about animal stats and abilities (though those help) and more about the DR 10/Silver, I think (though any other movement speeds are part of it too). When I played a lycanthrope the GM Had it have the reduced DR of an acquired and made the form changing slower like an acquired (though I didn't have to make the save). Then again, the situation for that was a little different anyway (It was technically acquired, but as a gift through a ritual by a clan of werebears rather than inflicted by bite).