Transitioning from After Effects to Motion

My recommendation is to create project that's long enough to handle your 10 sequences... sequentially. Set markers on the timeline to set the time limits for each sequence. Objects placed in the timeline can all have in and out points. Grouping the sequences will help in setting in/out points because this can be done, once, for all the objects in specific groups by selecting the group, setting the out time with the playhead, and typing the 'O' key to set the out point; then move the playhead to the beginning of the sequence time and type the 'I' key to set the in point.

If you're using Final Cut Pro, then there is nothing easier than a single project for each sequence. These can be created as Generators or Titles (titles have a "low profile" in FCP storylines) and simply applied when and where needed in FCP. There is absolutely NO NEED to render out any video. Motion projects are MBs smaller than their rendered video counterparts. No need to waste valuable hard drive space.

It's actually quite a bit more efficient to make these sequences as short as possible because it can be really "obnoxious" to have long animations applied to the storyline.

BTW, you can manage your sequence projects for FCP by saving them to a Theme Category. It makes them really easy to find in FCP (categories are automatically listed in the various inspectors) and keeps them all together regardless of their names.