Honestly I think Nagato(in his body) is stronger than Base Hashirama. And, yes, nagato who could walk before he fought hanzo did know 6pop abilities. He used shinra tensei against hanzo in the first place.
Hashirama and nagato's stamina should be roughly around the same level seeing as hashirama is a senju and nagato is a pure uzumaki. Now, when it comes to powerhouse attacks, hashirama has his mokuton, but nagato is capable of countering it with summoning, asura and deva. Let's not forget how much work the kyuubi did against hashirama. If we were to add cerebus, pterodactyl, rhino, chameleon and bull, nagato has a very powerful summoning fighting force.
The flight of the pterodactyl and the invisibility of the chameleon would be very effective in evasion. The immortality of cerebus would serve extremely well for defence along with the teddy bear. While the rhino and bull, and possibly even the centipede and crab could form a good attack. With all the summonings, hashirama would be expending copious amounts of chakra to fight them effectively while splitting his chakra into mokuton bushins to reduce the numbers disadvantage. With this, animal path has hashirama in a pretty tight bind and he is susceptible to the might of BT, ST and endless rockets. With all this overwhelming force along with Naraka path for healing, Nagato is near undefeatable by hashirama. Infact, it's very likely that (out of SM) hashirama won't even be able to find nagato on the chameleon, and he'd be completely opened to surprise attacks. FTW, BoD, Tree World, mokuton dragon, Mokuton bushin and mokuton appendages all become useless. Hashirama's only hope would be to enter SM at which point he'd be able to win.
This fight would eventually go towards hashirama as SM is nagato's true weakness. And, seeing as hashirama gains sensing, healing and powered up attacks, nagato's summonings and path abilities would become completely overwhelmed. Nagato would have to resort to an extremely large CT, but without intel he would have no idea about the size of Shinshuu which would be big enough to break out like the kyuubi did. For that matter, even with intel, Shinshuu's size is so massive that, if CT can even pull it in the first place, it would be able to shatter the core through a long series of 1000 palms.
I'd put nagato > Base hashirama but < SM Hashirama.
obito
hashirama
nagato
EMS madara <--- Yes, Nagato is able to take on EMS madara :| EMS isn't defeating rinnegan, especially when PS attacks are filled with chakra, along with the fact that nagato's arsenal counters madara's. The cerebus alone would be overwhelming for susano'o as the more madara slices it, the more it'd divide. Madara simply sends Cerebus after PS while he sits at the base and slowly preta's PS away, keeping a few summonings and asura limbs as extra defence with his ST.