First point I would like make in advice would be not to pay much if any to attention to battery packs you currently use in looking for a second or upgrade Nikon. Battery packs can be bought at reasonable prices! Well unless buying D4 batteries, thedn you will have purchased a highend nikon and the battery price will fit the cost of the nikon! Lol
Second, I am a hobbiest and currently use two bodies and have tended to own at least two Nikon DSLRs almost from the beginning! Also I have used battery grips right from the start and I have always recommended them for comfort and ease of using, besides the obvious advantages of longer shooting times without pausing to change batteries!
Now OEM vs third party, I have found I prefer OEM when possible, but I will buy and use third party grips when no OEM grips are available for the model Nikon I might have! There is no OEM grips for your D3200 so I would look into third party grips to see what others recommend in brands! If interested that is!
I'm a two Nikon DSLRs shooter, and always have tended to keep at least that many on hand all the time, but that is me! There is nothing wrong with going with two entry level DSLRs, though I tend to prefer moving ever upwards in one way or another when buying second Nikon when I can. But two of the same model can be very handy for sure especially if you have lenses you love that won't be safe to use on different body models! As you have a non ai lens, you might want to consider that.
You seem to have some pretty good glass, so adding as body might be a great idea if you feel the desire/need as I have felt many times as others keep teasing me about! Lol
But better glass is always a good option, and a good ultra wide lens can be very handy! For DX I think my choice for price vs quality would be the Tokina 11-16 lens from seeing my buddies work one!
I hope my ramblings will be of help! Also welcome to our Nikonites family!
