Becoming the Monster

[Anthrowhale]

A bipedal octopus with hands on 6 tentacles sounds kinda horrifying before you start adding prestige classes and other things.

Minor aside, but you may only end up with only 2 of the tentacles functioning as hands.
The operative bits are:

An anthropomorphic animal has the natural attack of the base creature, but it can also use weapons if it did not have hands already.

and

If the base creature has more than 2 limbs, the anthropomorphic animal has the same number, but two of them become feet. Thus, an octopus man, for example, would have only 6 natural attacks rather than 8.

All that it says about weapon use is that it can "use weapons". Plausibly that means at least 2 hands or other dextrous equivalents. More than 2 is consistent with the rules, but I don't see anything preferring an interpretation that there are 6 hand equivalents. The rules appear underspecified.

(Note though that at high levels you could get some gloves of man.)