Unlimited. JioPhone comes with 4GB Internal Memory - so, you can store as many contacts as you want, depending on the free memory on the phone.
JioPhone does support the JioChat messenger application.
It does take about 2 hours time to fully charge the JioPhone's 2000 mAh battery.
Yes, you can type message in the Gujarati language in the JioPhone.
Yes, the JioPhone does support the Hindi language.