Japan in summer

Hello!

Me and my fried are planning on traveling to Japan this summer. Since we are still students, we have holidays from mid june until september.
I was wondering when in that time frame would it be best to travel to Japan, so that we can get the most out of our trip (eg. see the most interesting festivals etc.).

June: Rainy season, but lots of flowers, especially hydrangea, which are one of my favorites. Quieter time since there are no Japanese holidays then... although occasionally school trips. But those are usually May or September. Rain cools things off, but getting quite hot and humid.

July: Tanabata, getting busy because the last week or so school lets out, so things get crowded. Start of the summer festivals. Hot and humid.

August: High season, lots of crowds, all the kids are out of school. Summer festivals in full swing, Obon holiday is extra booked so be careful, but also lots of festivals for Obon. Tohoku's Tanabata matsuri. VERY hot and humid.

September: probably most festivals have finished, but the kids go back to school. Still hot and humid. Tsukimi is this month as well.

We were originally planing to travel from mid July until early August. As far as I've read, mid July is when the rainy season ends. We do not mind the hot and humid weather as much, so as long it won't rain I think we will be able to make due.
As for the festivals, as far as I understand, there are many local festivals happening at that time. If so, how do I find them? I know about the large ones, such as Gion Matsuri, Tenjin Matsuri... But I am not sure which are worth visiting and if maybe there are some less known, but pleasant ones happening at that time.
Also, I would like to know if there are any must visit events going on at that time which would be near our planned route (Tokyo - Kyoto - Osaka). We will be traveling for 2-3 weeks (on that note - is 2 weeks enough to experience the most of what Japan has to offer?)

As far as I've read, mid July is when the rainy season ends

Usually, but that doesn't mean it doesn't rain. Also, rainy season rain is a lot different from summer rain. You may get rained out in a summer rain; for rainy season rain a rain jacket or umbrella will serve just fine.

As for the festivals, as far as I understand, there are many local festivals happening at that time. If so, how do I find them?

http://www.japan-guide.com/e/e2063.html
http://www.jnto.go.jp/eng/location/festivals/
http://www.japan-talk.com/jt/new/matsuri-list

etc. etc.

When you settle on dates, do a search and find the ones you're interested in to plan your trip around.

on that note - is 2 weeks enough to experience the most of what Japan has to offer?

No. But I've lived here six years and haven't experienced the most of what Japan has to offer, so you'll make due. It's best not to pack a ton of stuff into one trip anyway; better to miss some stuff but enjoy fully what you're able to.

Here is my rough draft of what I wanted to do in August of 2014. I believe that all the links still work, and that some have been updated.

Jul 16: Kyoto, Gion Matsuri
http://www.japan-guide.com/e/e3942.html
Jul 17: Kyoto, Gion Matsuri
Jul 18: Hanyu (near Tokyo), Chochin Toro Matsuri in nearby Kuki
http://www.goldenjipangu.com/140712kuki.html
Jul 19: Chichibu, Chichibu Kawase Matsuri
http://www.goldenjipangu.com/140719cicibu.html
Jul 20: Tokyo, Ueno Summer Festival Parade and Hula Festival
http://www.goldenjipangu.com/140719hula.html
http://www.goldenjipangu.com/140720ueno.html
Jul 21: Atami, Beach day with Atami Fireworks
http://atami.web.transer.com/bb_url_ej.php?ctw_=sT,eCR-JE,bF,hT,uaHR0c...,
Jul 22: Atami, day trip to Hakone to do the round course.
http://www.japan-guide.com/e/e5210.html
Jul 23: Amanohashidate (one of Japan's three most scenic place)
http://www.japan-guide.com/e/e3990.html
Jul 24: Amanohashidate, Monjudo Festival and Fireworks
http://www.kyoto-kankou.or.jp/english/info_search/?event_id=2312&r=133...
Jul 25: Osaka, Tenjin Festival
http://www.japan-guide.com/e/e4023.html
Jul 26: Tokyo, Sumita River Fireworks
http://sumidagawa-hanabi.com/index_eg.html
Jul 27: Atami, Izu-Yugawara Samba Carnival and Fireworks.
http://www.goldenjipangu.com/140727izu.html
I am not sure on this one. It was held on Saturday 27th last year, and it might be held on the 26th this year, so I might end up having another beach day, and going to the Abegawa Fireworks Festival in Shizuoka.
http://www.goldenjipangu.com/140727abegawa.html
July 28: The World Cosplay Summit in Nagoya.
http://www.goldenjipangu.com/140727nagoya.html
http://www.goldenjipangu.com/140727oyama.html
July 29: There was a Yokakoi Dance Festival in Wakayama, which is south of Osaka.
http://www.goldenjipangu.com/140729kishu.html
July 30 & 31: Stick around Osaka and do Universal Studios, or go to Kyoto for the Temples, or, do the beach at Shirahama (further south).
http://www.japan-guide.com/e/e4958.html
Aug 1 - Osaka - PL Art Fireworks (Possibly the largest fireworks displays in the world)
http://en.wikipedia.org/wiki/PL_Art_of_Fireworks
Aug 2 - Nagaoka - Festival and Fireworks
http://www.goldenjipangu.com/140801nagaoka.html
Aug 3 - Akita - Kando Matsuri
http://www.japan-guide.com/e/e3627.html
Aug 4 - Aomori - Nebuta Matsuri
http://www.japan-guide.com/e/e3755.html
Aug 5 - Sendai - Matstushima Bay tour boat, Sendai Fireworks
http://www.japan-guide.com/e/e5100.html
Aug 6 - Sendai - Tanabata Matsuri
http://www.japan-guide.com/e/e5158.html
Aug 7 - Otsu (near Kyoto) - Tanabata in Kyoto
Aug 8 - Otsu - Lake Biwaka Fireworks
Aug 9 - Kochi (Shikoku Island) - Yokasoi dance festival
http://www.goldenjipangu.com/140809kochi.html
Aug 10 - Miyajima (near Hiroshima) - 48000 Kannon Festival
http://visit-miyajima-japan.com/en/culture-and-heritage/cultural-herit...
Aug 11 - Miyajima - Miyajima Fireworks
http://www.miyajima.or.jp/english/event/event_hanabi.html
Aug 12 - Tokushima (Shikoku Island) Awa Odori
http://www.goldenjipangu.com/140812awa.html
Aug 13 - Tokushima - more Awa Odori
Aug 14 - Takamatsu - Takamatsu Matsuri and Dondon Fireworks
http://www.city.takamatsu.kagawa.jp/english/sightseeing/event/
Or... Osaka - Danjiri Matsuri
http://www.goldenjipangu.com/140814danjiri.html

This will give you an idea of what you could do. The Golden Japan website is fairly good for festivals. I have found that they will sometimes post the date from last years festival, and then update the date, when they get more information. IU have tried to include some of the big festivals, along with several smaller ones. My trip ended up getting moved into early July, but I still did several of the festivals from this plan.

I hope this helps.