You placed Jiraiya above Orochimaru. If Edo Tensei is included, then how the hell is Jiraiya stronger than Orochimaru?
Similarly, you placed Minato over Tobirama. Minato knows Uzumaki seals as an advantage against Tobirama but that's not so much as a battle advantage. Aside from that, Minato is just better than Tobirama at one thing, FTG, that's all. Everything else, Tobirama excels. Tobirama can also do FTG (not as good as Minato) plus so much more like KageBunshin (he developed it) and other Senju techniques (Tobirama lived in war era unlike Minato). And most importantly he has Edo Tensei. He can solo Minato easily.
Minato was also faster in Shunshin as Edo Tobirama praised and this is without SM enhancements. Both are sensory type with Tobirama showing to be more skilled with his. Minato does have a large reserve since SM training requires it but Tobirama has more no doubt. This is a close fight not a neg but I do see Tobirama winning since he does have higher skills in other departments, higher reserves, and even if Minato is more skilled with FTG, I can see Tobirama using FTG with his water jutsus as Minato uses his Kunais.
If Jiraiya goes SM and uses Frog song then it wouldn't really matter that Orochimaru summoned the Edo's would it? If he catch all of them in it then both their minds and bodies will be paralyzed which gives Jiraiya time to seal the Edo's and kill Orochimaru (he can also turn them to frogs after frog song). So it all depends really since Jiraiya was able to take on the Peins; first 1, then 3, then all 6. The summoning Pein alone was taking out Jounin level ninjas so each body is between Jounin to Kage level.
Eight Gate Gai (no powerups or upgrades, only hard work)
Hashirama
Orochimaru (since he can summon Tobirama, Hiruzen and Minato whitout Kurama)
Using the gates is a powerup, it literally power you up by giving you access to more of your chakra by removing chakra limiters. Also the gates doesn't make Gai able to be the likes of Tobirama, Madara, and Hashirama. Opening the 8th gate is said to give you power over the 5 Kages, Edo Madara (holding back and seeing the fight as child play) easily took out the 5 Kages so I don't See Gai being on EMS Madara level. Let's put it this way, Gai base is Jounin level yet he had to go 5th and 6th gate against a clone of Kisame who had 30% his chakra which became 7.5% after he made 3 clones to restrain Gai's team. Then he had to go 7th gate against a weakened Kisame who didn't have Samehade so 7th Gate puts Gai on Kage level with 8th gate putting him a level above that. Tobirama, Madara, and Hashirama are about 2-3 levels above Kage level.
The gates is the same as SM then since you have to go through intense training for both and both gives enhancements. Same with Prefect Jinchuurikis since it's hard work to learn to use the Bijuu power, gain their trust, use their chakra control which is harder for them than non-Jinchuurikis, and tons of risks such as the Bijuu taking over their body/losing the Bijuu kills them/they can be viewed as weapons/monsters, they can hurt their comrades.
By base i mean the stuff you are born with, genetics. No cheating, no borrowed/stolen powers, no experiments, no jinchuuriki's. Example, Sasuke would never even have gotten EMS or even the curse mark and Naruto would never have been a jinchuuriki or gotten Hagoromo's upgrades. Madara would never have gotten EMS, he would be MS Madara for life. No stealing cells etc. You get the point.
Only what you learn, are taugh, train for and good old fashion genetics count.
Summons do count, it's a jutsu you have to learn and you need a bond with the summon. And YES, edo summoning does count, it is a jutsu one must learn and master. Weapons and tools are of course allowed. And yes, you can summon and controll a jinchuuriki if you have the power/skill to do so.
You need to use your imagination on this thread, we are imagining that everyone is living in the same era. Everyone are at their prime. And also we have to imagine how powerfull the likes of Sasuke, Obito, Shisui and Naruto would be at their prime.
So this would be my list: (No aliens allowed)
Hashirama
Madara
Hiruzen
Jiraiya
Itachi
Minato
Obito
Shisui Uchiha
Orochimaru
Onoki/Mu
Sasuke
Fourth Raikage
Naruto
Might Guy
Tobirama
Tsunade
Well Hashirama would be the strongest then since his base was fighting EMS Madara+Kurama for a good while until he got serious. Hashirama also had all Bijuus but the 1 tails under his control so he has 2-9 after taking it from Madara. Also you do know that Ashura's descendants have the Sage's body which lets them be able to handle having the Bijuus seal in them just like how Indra's descendants have the Sage's eyes which lets them control the Bijuus.
Your title said base so that means no SM, Chakra gates, Bijuus, Doujutsus, or anything that gives enhancements besides the chakra they normally have. That would still make it Hashirama as the strongest unless current Naruto is as strong or stronger than base Hashirama.