Re: Tobirama takes down prime Kabuto
First, Kabuto's Sensory skills will help prevent complete death against FTG. but more importantly, even if he is hit, Oral Rebirth saves him.
Kabuto absorbed Suigetsu's DNA making him capable of hydrification: Making Suiton useless. He additionally has Karin's rapid healing ability in case FTG does cut. Even then, he also has Kidomaru's DNA for Iron Skin (Golden Web armor), and Kimmimaru's DNA to harden his bones.
Second, Edo Tensei as used by Tobirama is theoretically useless against Kabuto. While yes they have incredible blast Radiai, Kabuto is a sensor but also an Edo user. Meaning he's going to simply use his enhanced speed to retreat. Tobirama's Eros have nothing other than the suicide bomb. Kabuto's Edo Tensei are more powerful as they have actual abilities and rational thought. If they break the upper half of the edos, they can't self detonate. Also, Tobirama does not have any prepared FTG Kunai. Even if he did, Kabuto has attacks to destroy them.
Tobirama with a few explosives can't hold out against Kabuto's Edo Tensei army. Besides, the number of edos Tobirama can make has never been clarified. To Sasuke they can equalize is a fallacy.
Tobirama is still susceptible to White Rage and the Sound Genjutsu. With infinite Senjutsu collection (Juugo) he almost has infinite stamina in some regards.
Also... You did mention PRIME Kabuto meaning he had Madara and Itachi as well. Though he'd have to simplify Madara.
BASICALLY... This is the match you've said Tobirama wins...
Tobirama, Undetermined amount of suicide bombs
DSM Kabuto, Madara, Itachi, Nagato, Kakuzu, Deidara, Sasori, Hanzo, Chiyo, Sai's Brother, Kimmimaru, Mist Sensor, Hizashi, Ginkaku, Kinkaku (people he had trouble with already), Asuma, Dan, Zabuza, Haku, Pakura, Gaki, Kushimaru, Jinpachi, Ringo, Kisame's sensei, Mangetsu, other Mist Swordsmen I can't remember the names of, Magnet release using Cloud Edo, 3rd Raikage, Muu, Trollkage, 4th Kazekage, Hanzo, and dozens of other notable Shinobi
Kabuto has numbers, Elemental advantage, Intel advantage, scale advantage.
Kabuto defeats Tobirama.