Yes, You can use a MicroSD card up to 64GB in the JioPhone.
It does take about 2 hours time to fully charge the JioPhone's 2000 mAh battery.
Yes, the JioPhone does have FM radio. In fact, it is wireless FM radio. You do not require to use the earphones to use the fm radio.
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.