Yes, you can use the 4G Jio sim card in Comio C2.
It takes about 4 hours to fully charge the Comio C2. That is because it has huge 4000 mAh battery. If you use any good quality fast charger - the charging time can reduce by almost 35%.
No. Since Comio C2 has 4000 mAh big battery and to avoid heating issues, company has used high quality Polycarbonate body.
Yes, Comio C2 does have the front camera flash.