Newbie question

Hey y’all, new seller here. Hoping I have something solid to give back this community soon as I’ve learned so much online already.

Here’s my question. I have a largish quantity (maybe 500 each) of 2 configurations of an item that I would like to sell to get some seed money. The items are two sizes of stainless lunchbox’s.

TL;DR: I got these items for free (well other than some heartache) because they were purchased by my ex through his wholesale business and sat in my garage for 2 years. He ain’t coming back for them! They are legally mine per our divorce agreement stating what possessions he can take from our house.

So, I feel like the quantity is large enough for FBA and the demand is there (I need a little more research into pricing) however since I have no real documentation around the source of the product.

Since I have these items for free, the only thing I really have to lose is an mis step with Amazon that would prevent me from a larger operation later. For now I just want to sell what I have while to get some seed money and learn what selling on Amazon is like as I build my brand and set things up in the background.

For this unusual situation, is FBA the way to go, or should I merchant fulfill to get things going?