No. Gionee A1 Plus is not a water-resistant phone.
Yes, Gionee A1 Plus does support OTG.
No. Gionee A1 Plus video recording is restricted to 1080p resolution. You can record Full HD videos but you cannot record 4k videos.
Gionee A1 Plus is a fully metal body phone and it does support fast charging, too. Besides, it has huge 4550 mAh battery. So, you may notice a minor heat issue while charging the same but otherwise there were no heat issues reported during our review.