PH lady and JP man marriage

I'm a Philippine lady 28 years old with tourist visa 90 days & my 2 years boyfriend was a Japanese 32 years old.
1. We planed to get married in Japan & Philippines next year.Is't possible?
2.Does anybody here know what documents should we bring before and after marriage?
3. Could we have dual citizenship?

1. We planed to get married in Japan & Philippines next year.Is't possible?

Sure, but you'll have to pick one country to legally marry in (and then maybe register in the other). Look into it, but I believe it may be beneficial to marry in Japan rather than in the Philippines due to registration rules and the ability to divorce.

2.Does anybody here know what documents should we bring before and after marriage?

Depends on where you marry and where you intend to live afterwards.

3. Could we have dual citizenship?

No, but your children could.

From the Wikipedia page on Japanese Nationality Law:

It is generally difficult to have dual citizenship of Japan and another country, due to the provisions for loss of Japanese nationality when a Japanese national naturalizes in another country (see "Loss of citizenship" above), and the requirement to renounce one's existing citizenships when naturalizing in Japan (see "Naturalization" above).

There are still some ways in which a person may have dual citizenship of Japan and another country, including:

They had dual citizenship prior to January 1, 1985, when the Nationality Law was enacted
They acquire multiple citizenships at birth, such as being born to a non-Japanese citizen parent and acquiring that parent's citizenship as a result of that country's laws or by being born in a jus soli country. However, they must choose one citizenship/nationality before the age of 22 or within two years if the second citizenship is acquired after the age of 20, or they may lose their Japanese nationality (see "Loss of citizenship" above).

Thank you.
after marriage what visa should I get so I can stay in Japan more than 90 days ?

A spouse visa. Maybe you should do some research with your partner. You can talk to your respective countries' embassies for more information.

Your boyfriend is Japanese, right? Why doesn't he ask to immigration of his country? He speaks, read and write Japanese? Guess he can look for information in Japanese from people who were in same case...

Guess you can look for information in English from people who were in same case... Oh wait...