While it might be nice to have the lid, it is not always necessary as it should be compatible with the from the bowl that comes with the mixer, but DY is right about trying to find the best deal to get the whole thing at one time, especially if one knows that s/he is going to use primarily the metal bowl due to the use of large amounts of flour to make challah.
I do want to ask Yazmitch a question about the cookie paddles – I have had those in the past and have had problems because the plastic attachment onto the metal piece that goes over the bowl has broken. I’ve had not only one set, but more than one. They’ve not been available here in EY, so I’ve had to order from US and had brought over by a friend/relative who is coming. Sending back is too involved for me to deal with so I have not managed to use the “guarantee”. Are they coming out with newer ones that have metal for the attachment or did I misunderstand your post? They are great for making large batches of cookies – I have done triple batches of chocolate chip cookies before and they are also good for making large batches of brownies since the dough is thicker than the whips can handle and you don’t need the dough hook for such things, so the cookie paddles are a great in-the-middle item. Perfect attachment to buy off the bat if you will be doing baking for simchos or just want to get a lot done before YT.