UMA does nothing special with animations so any generic or humanoid animations can be used with the appropriate rig.
Making new clothes for a race involves taking a mesh, skinning it to the target character's skeleton, then importing it in to unity and creating slots, overlays and a recipe for it. The first step will be very dependent on the modeling software you use.
A whole new race can range from simple to complex depending on the features to support.
Without supporting runtime bone deformation for a race, then a skinned mesh with a valid humanoid (or generic) skeleton is almost all that is needed.
Both a “unified” version and a “separated” version of the race is recommended (though not needed). The unified version is a single connected mesh. The separated version is with cut, separate meshes for individual body parts that can be set later in UMA to be individually hidden or not. For example, separate mesh for head, torso, hands, legs, feet, etc…
The unified version is then used when building slots as a “seam” mesh, which means the normals from it will be used instead of from the individual cut up meshes. The cut up meshes tend to distort the edges of the mesh and then will not look correct when lined up with their neighbors.
To create a valid new race, you will need to create a RaceData asset, a base recipe for that race, and a T Pose asset.
The base recipe is a standard TextRecipe of all the race's default slots and overlays. This will be added to the corresponding field on the RaceData.
The T Pose asset is extracted from an FBX of this race with it's full skeleton. After configuring the Mecanim Avatar that is standard in Unity, then you can use the UMA dropdown function “Extract T Pose”. This will create a new T Pose asset for your race that you can add to the corresponding field.