Since you know how to load and retarget a bvh animation, i will try to explain how to use the nla editor to play some actions in a sequence
First you might want to open a dopesheet editor and set its mode to
Action Editor. Every time you load a BVH animation the current action gets replaced by a new action. However every action uses the fake user (the background of the F-Button is darkened) and thus remains in the blend file even when its saved and reloaded.
By clicking in the second highlighted box you can choose the current action for your animation. When you are done and loaded all animations you want to enqueue, press the button to the right to unlink the action from the armature. It should look like this.
Now open the NLA editor. You can also choose and unlink the action in the Properties Panel (Press N to toggle it)
Add -> Add Tracks from the Menu below. Move the cursor(green line) to frame
0 (click and drag) and choose
Add -> Add Action Strip where you choose your action you want to play first from the dropdown menu. Move the cursor beyond the yellow bar representing the action strip and add your next strip.
It should look like this afterwards
You can add additional tracks and stack them. The options for blending the strips can be found in the Properties Panel
You might want to create your own actions and only keyframe specific parts like the root bone and put it on top of the stack to override and control the motion.
For further informations see NLA Editor. Here is a link to a video showing the steps described above.