Mechanically, Jelly Form already gives you the benefits of the Tentacle Mass and Tentacles merits, though you could take Tentacles a couple of times if you wanted to get a higher bonus to your Restrain skill.
You also already get any of the cosmetic effects of Altered Genitalia that you want, so your tentacles can already be cocks, should you want them to be. Taking the merit would get you the mechanical benefits, though, things like Locking, Stimulating, DP, and so on.
Assuming you just wanted Incredible Size, Aquatic, and Venom, though, that would require an extra three points in flaws to pay for it. Looking over the list now...
Compulsive Masturbation could lead to some very fun scenes. That would also get you two points, right there. ^^
There's the aforementioned Addictive quality, which would get you one point, and you could have a Crush, which would get you another point. You could have a Reputation for another point, and if you want your character to be in Denial about having a given fetish, each one would be worth another point.
You could have Enemies for one point, a Phobia would be worth two, being Unlucky would be worth two, you could have an Evil Twin for one...
See anything that might fit?