Okada Masahito wrote a great piece on Saito Dosan on the Nobunagagaku blog called Mamushi no Dosan. Even though the essay is in Japanese, I highly recommend that you read it.
Here is the link: http://nobunagagaku.com/cn16/essay04_01.html
I am still reading Ehata's Okehazama book and found something interesting that fits with this post. On pages 288-89, he mentioned that there was a possibility that Nobunaga had 250 soldiers with bows and 250 with guns during his famous meeting with Saito Dosan at Shotokuji Temple in 1553. That caught my attention right away. To tell you the truth, I do not know if it was true or not. My humble opinion is Nobunaga had at least 500 gunners with him when he met his father-in-law.
Tenka no tame!