I mean it could work if you are willing to give up the waveclear provided by minion dematerializer. Personally I wouldn't go for it though.

BTW, how can I put doran's ring with the image and all informations?

Doran's Ring vs dark seal
dark seal gives more mana, almost same ap, more heal from corruption, and you can totally snowball. Dorans ring just gives you 60 hp + 15 ap, (the mana passive is unique), so dark seal give more sustain, more snowball potencial and a litlle less AP(7 vs 15 AP).
And this is what lol wiki says:
If you use your three Health Potion item potions, you're getting 112.5 health from this item's passive effect. This is 52.5 health more than Doran's Ring item Doran's Ring and increases its value to Gold 766.25, making it 218.93% gold efficient.
If using a Refillable Potion item Refillable Potion instead, it provides 62.5 health, making the item worth 586.25 - a gold efficiency of 167.5% - increasing by Gold 228.75 with each back.
As you can see, this is a lot more efficient then double doran's ring.

No, it does not. If you read the description it'll tell you that it does true damage based off of level and has no scaling off of any AP or AD one might have.

Hello!
I tried multiple choices including electro in the past and no - it's totally not worth it. And when I am looking into your build and knowing how the champion works, I don't see it being better than current build. In plat elo you might've found success with it, but fact is that with this build I am cappable of stomping plat games. But obviously if the build fits you, it's all fine and keep it up!

AD Kogmaw has usually lifesteal + support that mainly protects him. As AP, support usually protects his own ADC, while you are standing a bit more behind, sometimes out of position from your team. In addition - AD Kogmaw might build some extra tankyness like Frozen Mallet, Vits end and such - you can't do that as AP - you can possibly build one item, but that won't give you that many defensive stats. For W it doesn't work like that mainly because AD Kogmaw is usually building Rageblade that doubles his W effect + he has way higher attack speed than AP + he usually builds Hurricane, that allows him to shred multiple targets at same time.
For spellvamp part - you can't really omit any items off your build in order to get spellvamp, without sacrificing too much. I tried to go in that direction, but fact is that usually you are either way full or dead - if you are standing behind and keeping your position properly, you usually don't really need sustaining yourself and if you get hit by stuff like Syndra E, you are gonna get obliterated. Sure, sometimes it might save you in certain situations, but still as I said - you would lose too much.