whoever want to know this is a spoiler!
but anyway no roxas isn't in birth by sleep
however ventus, one of the protagonists of bbs is related to sora and in turn roxas.
Since you are referring to Kingdom Hearts 3 as Birth by Sleep yes but that isn't actually Roxas, that's a character named Ventus
Roxas first appears in Kingdom Hearts II.
Roxas is Sora's Nobody.
roxas is the nobody of sora, originated after sora released his heart in Kingdom Hearts I
Roxas appear in Kingdom Hearts video games. These can be bought for 3DS, PSP, Play Station 2 and 3. There are several games in the Kingdom Hearts series, such as Kingdom Hearts: Birth by Sleep and Kingdom Hearts: Chain of Memories.
No
Yes, he will be voicing roxas in kingdom hearts II.
No. The battle between Sora and Roxas is merely a cutscene in Kingdom Hearts II. The actual fight against Roxas is only available in Kingdom Hearts II Final Mix+.
Roxas is considered to be in 2 of the Kingdom Hearts games. He is the main character in the beginning of Kingdom Hearts 2 and then he is the character you play as in Story Mode in Kingdom Hearts 358/2 days.
no, not without modifying your game. you can only play as Roxas in the beginning of Kingdom Hearts 2. if you want your fill of more Roxas then i recommend buying Kingdom Hearts 358/2 days. you play as Roxas through the whole game!
yes
I'm not sure. It's supposed to have Sora and Roxas in it, and also The Keyblade Wars!! New characters, new story!! Go to youtube.com to see a video of it. Kingdom Hearts 3 The Keyblade Wars For: Plastation 3