A rear cinch is not really required. Depending on the design of the rigging system, it is better to have it. But, you can likely get by without it.
So, you mean a riser pad to lift at the shoulders? I always think of a riser pad as teh one that goes to lift the rear up.
Have you laid it on your hrose yet?. Does the fork (the arched part under the horn) sit down on the wither? How many fingers can you slip between the fork and the wither, after cinching it up?