Fluid models rendering with gaps was a known issue that was fixed in Forge 1.11.2-13.20.0.2279. It's very unlikely that this will be backported to 1.10.2.
The model loading for the inventory variant not being loaded is probably due to you adding a blocks/ prefix to the model path. I'm guessing your blockstates file is assets/sw/blockstates/fluid/plutonium.json, not assets/sw/blockstates/blocks/fluid/plutonium.json.
You can use forge:fluid as the item model if you want the item form to render as a 2D-style square with the fluid's texture. Having the item form look like a bucket may be confusing, since it wouldn't actually be a bucket.