How good is "good"? It would almost have to be free for it to be a great deal because, as you said, you are using a BMW shop to do all of the work. This will be a few thousand in labor on the suspension components and prep that you will have to pay for again to move it over. Just the engine work alone doesn’t justify the cost.
Donor 325 - $500 (that’s what I consider "a great deal"
Used Engine - $500
Engine swap Labor - $600
You already have at least $1600 in converting a 325 to a 325i. Forget the swapping of stuff, you’ll have spent more in the long run when you could have just continued searching around.
I looked around for about 3 weeks and last week I picked up a pretty clean 325is for $1100. Very solid, tight car with 163K on it. Has a rub in the fender and the front spoiler is gone but is mechanically excellent.
Keep looking until you find the right car.