Eluga A3 does have 3GB LPDDR3 RAM.
You can use one micro and one nano sized sim card in Eluga A3.
Panasonice Eluga A3 comes with 5.2 Inch HD IPS display with 1280 x 720 resolution which produces 282 PPI resolution. It has Asahi Dragontrail Glass which provides protection against scratches etc.
Yes, Panasonic Eluga A3 does have support for the OTG.
Panasonic Eluga A3 does come with Fast charger. To get the fast charging, you need to use the company provided charger.