1. I dont think DB's will cause the shoulder pain, but rather poor form. DB's are easier on your shoulders than BB's.
2. Yes they are as effective, if not more. Besdies if you choose you can go deeper with DB's.
3. The only good thing a smith machine is good for is hanging your coat and that will be the most common answer about that here.
4. This is a bad routine, reason being way to many isolation exercises and you are going to failure much to often. I would go for 10 reps with a 12rm. Meaning do 10 reps with the weight that you would if you were shooting for a max of 12 reps. Something much simplier would work much better like:
DB Bench-3-4 sets
Incline Press or decline press-3 sets
Simple little routine. You are doing far to many sets looks like 16 sets for chest, imo I wouldnt go no more than 12 for chest and maybe fewer, especially if you are lookin at very many sets to failure.