While I'm tempted to just post my Senior Thesis here, because it was exactly on the Japanese Teppo or matchlock in the Muromachi and Azuchi–Momoyama eras (Esentially from ~1337 C.E. to 1600 C.E.) I'll try to answer your question point by point and add some more background when i can.

I'll start from the beginning and work my way though your questions along the way. The Japanese peoples probable first encounter with gunpowder based weapons is when the Mongols tried to invade in 1274 and 1281 C.E.. These devices were primitive and were closer to grenades or mines than anything resembling a matchlock or musket.

The next encounter with gunpowder that japan would likely have was at sea from pirates in the early 16th century. This was made possible by the Portuguese taking the Fort at the Malacca Strait and moving from there upward toward Japan. However it was the a Chinese Junk that was damaged off the coast of Tanegashima Island in south-west Japan on September 23, 1543, that arguably brought the first matchlock to Japan. The Teppoki or Record of the Musket, was the account of the interaction between the crew of this ship, the lord of Tanegashima and their interaction with the new weapon. Soon after this they were able to poorly copy the new weapons but after another ship came close with a Portuguese Blacksmith they were truly able to perfect the weapon. To answer your question about the differences between European and Japanese matchlocks of the period, the Japanese esentially copied the European design but that design was likely from an Armory built in Goa, India, conquered by the Portuguese in 1511. So by the time the got the weapon in 1543, they likely would have been inferior to the matchlocks made in Europe.

To answer the tactical question, they were usually deployed behind cover and had a limited effective range of about 50 meters. http://en.wikipedia.org/wiki/File:Ashigaru_using_shields_(tate).jpg This picture from Wikipedia show's how they would likely have been deployed. The first person to take full advantage of the Matchlock was Oda Nobunaga, where he used their skill to defend Nagashino castle, at the aptly named battle of Nagashino.

As for you first numbers question, Hideyoshi, the second of the great unifier's, launched an invasion of Korea in 1592 with roughly 200,000 men. Roughly half of them were thought to have been equiped with period matchlocks. This would probably be the high number for the period, so ~100,000 would be a decent guess. As for their effectiveness, the Japanese army took Soul, South Korea in less than a month and they were highly effective against the Korean forces because they had not seen them used in mass and effectively. The Koreans with the help of the Chinese would eventually push them out but the Japanese held their own. Hopefully this isn't too long and answers most of your questions.

Some Refenences.

Lidin, Olof G.. Tanegashima: the arrival of Europe in Japan. Copenhagen: NIAS Press, 2002.

If there is any book a recomend on the subject that isn't in Japanese it is this one. It has tanslated versons of the Teppoki and the Tanegashima Kafu or the history of Tanegashima Island.

Swope, Kenneth. A dragon's head and a serpent's tail: Ming China and the first great East Asian war, 1592-1598. Norman: University of Oklahoma Press, 2009.

This book is about the Hideoyshi's Korean war and has some but not a great amount of detail on the subject or matchlocks.

I find that claim incredibly orientalist exaggeration. And really Extra History's Sengoku Jidai is not their best work to say the least (there's zero use of new research, and lots of sensationalist fluff instead of accuracy).

Japan had about 200k firearm from the 17th to mid 19th century. Considering the tercio's ratio of guns to pike was 1:1 and the Spanish Empire alone (admitted the largest power in Europe at the time) had 300 000 men under arms, I find it hard to believe that the entire of Europe can not field 200 000 guns (though I would concede Japan probably had more guns than any single European polity, but it also had more population). Especially since Japanese battle formations even in Edo had less than 1:1 gun ratio due to a huge number of squires and other "semi-combatants".

Arquebus were lighter types used by Portuguese, mostly not requiring the stock support used in Europe. Their craftsmanship were recorded by traders as surprisingly well. Most armors could be penetrated at 50 meters (Japanese were not very well armored in comparison to Europeans). I've heard (but have not seen sources) that says later on they moved for higher accuracy but lower rate of fire. But other ignition systems like wheellock and flintlock were not produced, and the matchlock was used all throughout.

Tactics varies with period and place. And a lot of famous tactics in the past are called into question. But setting those aside, in a pitched battle generally arquebusiers worked in conjunction with archers, with archers providing covering "fire" while the gunners reloaded. They formed the front of the formation and seem to worked in small teams of less than 10, and did not stand shoulder to shoulder but a bit looser, with the team firing in volleys. When they just started to be used they softened the enemy for a spear charge. By the end of the Sengoku they...still did that but the spear men were almost relegated to protecting the gunners.
Some commanders also told their gunners to fight sitting down.