Firstly, it's not Kingdom Hearts 3, it's Kingdom Hearts: Birth by Sleep, made for the PSP console.
Secondly, they aren't Sora, Kairi and Riku - they're Ven, Aqua and Terra. Supposedly, they're counterparts to the three though and somehow linked to them.
The Gummi Ship feature was added to Kingdom Hearts II with extra abilities, weapons and an easier cutomization mode. Traveling to different worlds was also made much easier.
Kingdom Hearts (original) (English) Kingdom Hearts Final Mix (Japanese/English)
there are two ultima and ferir weapons
I believe there are 22 keyblades that you can obtain.
Kingdom hearts 3 isn't based on a different series, your thinking of birth by sleep which includes Terra, Aqua, and Ventus. Kingdom hearts 3 is going to include mainly Sora the (Creator said so) Edit: just to improve his answer Kingdom hearts birth by sleep is a upcoming psp title which is a prequel to kingdom hearts
The joke weapons are available in kingdom hearts 358/2 days, and give a funny looking weapon look to the character who wields it. Example is vexen's "pot lid" joke weapon in place of his shield.
There are currently 39 known keyblades as of Kingdom Hearts II.
Equip good items and weapons.
You can buy staffs and shields for Donald and Goofy, but not keyblades for Sora.
You can't buy it in the game, but you can try searching online for them.
They're two different people. Roxas, Sora's Nobody, is blonde. Sora is a brunette.
Kingdom Hearts Manga(published by TokyoPop) Kingdom Hearts (vol. 1-4)Kingdom Hearts: Chain of Memories (vol. 1-2)Kingdom Hearts II (vol. 1-4)Kingdom Hearts: 358/2 Days (unreleased)