
Sounds like you are rushing things with his obedience.
The Retrieve - I would find a club that uses the clicker, you will be amazed at the results for a dog that doesn't like to hold a dumbell. It is too complicated to explain if he is not already conditioned to the clicker. If he is conditioned to the clicker, tell me what sort of things you do with him and how and I will try and explain it further.
The Sendaway - Are you training with a mat? If you get your dog to go down near you on a mat, then you should be able to build it up by placing his mat a bit further away each time. The mat becomes a target that he lays down on. The mat is gradually reduced in size so it is only a few inches square in the end. Teaching the actual sendaway becomes a seperate exercise, send him to a marker with his ball firstly infront of it, then behind it, don't down him at this stage, just tell him to get it. Eventually his ball can be hidden under the mat and he gets it after he has gone down.
Sounds like you have loads of time to teach the sendaway so don't rush it, build it up very gradually so he is confident.
I know lots of dogs that do both competitive obedience and agility, so there is no reason why you cannot do both.