From your description of what you want to haul, it sounds like you are looking for freight cars? If so, the early 10 series freights are what would go with the brass No. 7: 11 flat car, 12 gondola, 13 stock, 14 box car, 15 tank and 16 hopper. They come up frequently on the auction site and at train meets. They have hook couplers, and their trucks are the same as what is under the tender that comes with the 7. The 100 series freights are too small and too low, they would not work well.
The MTH brass No. 7, 11-1018-1, comes with a combination coupler on the tender (hook and Lionel latch). So you could also pull the later 200 series freights as well, which have the latch couplers. They would not be "correct" vintage chronologically, but the 200 trucks are high enough to work, and they are sized okay for this loco, they are just a bit longer than the 10 series cars. The advantage is that you could find MTH new reproductions of the 200's easily.
For passenger cars, the early #29 day coaches and the 18-19-190 sets had the same trucks as the tender on the 7, and hook couplers. They were what the No.7 was sold with originally. MTH makes reproductions of the 18-19-190 set.
Personally, for what you are doing, I would try to find good old 10 series freights, or maybe better yet, ones in bad shape and repaint them. This may take some time however: as an interim measure, you could use MTH 200 series cars until you completed your set of 10's.
