I can potentially get this plane free, but it does have a small crack on one side of the mouth. Will it still work fine as a user plane?
Is the crack up the cheek (side) of the plane, or across the sole?
Either way, the plane will still work just fine, so long as it's not scratching the wood.
Often, cracks radiating up the cheek, from the corner of the mouth, will allow enough stress for the opposite cheek to crack, too. When that happens, the whole front of the plane falls off, making your #4 into an 'instant bullnose' plane.
#4's are common enough that it's really not worth repairing, so I'd just use the plane until it breaks. That might happen in two strokes, or in 20 years. No way to tell.
Get as much use out of it as you can, then put the tote, frog, iron, chipbreaker, and lever cap up for sale on Ebay. You may find that the parts are worth more on Ebay than a whole, intact, #4 would bring.