Jim O'C posted some great photos of the possible equipment you could use. I hope you won't mind if I add a few more.
I believe that this is the engine that you have coming. A Type XX engine #401 with a #421 Type IV tender
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As Rob mentioned you will have some difficulty making all of the different coupler styles work together. One option would be to match up an Ives tender that has the the same kind of latch couplers as the cars have.
The tender is actually a Lionel tender. Remember this is from the transition period when Lionel and Flyer both owned Ives. Some of Lionel's equipment was re-branded as Ives.
Here are the two American Flyer couplers that Jim showed above:
The tab and slot
and this is the curly cue, which American Flyer called its "automatic coupler" in 1938 and 1939.
The third coupler is the latch type which I believe is actually a Lionel coupler
Which type of coupler do your cars have? I'm guessing that you have the latch type. I don't think the 1700 series freight cars ever came with the Ives coupler. But I could be wrong
In any case this is probably what your cars matched with the equipment that you are waiting for will look like all together - if you can figure out a way to couple them together.
This is the Lionel #257 which was re-branded as an Ives #257 that actually came with your cars.
This is what the whole set looked like (from your original post it doesn't sound as if you have the matching Ives caboose in your collection).
I hope this gives you some ideas. Be sure to post photos when the package arrives.
Greg