1) You draw the correlation between how Hashirama dresses and how Mifune Dress. But Madara dresses the same way, that is just how the old school fighting clothing looked like. The samurai being based on tradition dint change too much, I say too much because they DID in fact change, Look at the samurai defending the 5 kage summit, they look nothing like mifune, but he being alot older does look and dress like alot of the older shinobi we see like Madara and Hashirama. That is just how they dress during that time, that is no reason to jump to any crazy conclusions, especially not to claim that anyone seen in said armor is a samurai...
2) Kisame used swords, there are also the 7 deadly swordsmen, kakashi uses a blade, so does Sasuke and Orochimaru, dozens of people in the naruto universe uses swords. To say Hashirama uses swords + Samurai uses swords = there best buds is another large leap.
Conclusion:
Your first argument was that because they dressed the same they must know each other, but now we know that that is just how people during the 1st shinobi war dressed, and thus that is no reason to assume they knew each other.
Your second argument was that samurai use swords and hashirama uses swords, therefore hashirama has a connect to samurai... pointed how wrong this was simply by stating all the people that also use swords but have no connection with samurai's. ALso it would only fit with hashirama's fighting style (wood jutsu) as he didnt actually use the weapons but he used tree limbs and branches to wield the weapons making them deadly, as just getting hit by a flying tree branch probably wont be deadly, it only makes sense for him to use weapons such as these.
With that said I am surprised you even thought you had enough to make a strong argument, 2 weak arguments dont equal a strong one. Better luck next time old friend.