I presume the seals you are talking about are the cam seals? I would replace them if they were leaking, if not then don't bother. The cam sensor I would replace if that is the code that is popping up, plus you are there anyway. Pulley bolts I wouldn't about them failing but if you want to that is your choice. Spark plug removal for timing belt replacement is a mechanic's choice I think. The serpentine tensioner is not a difficult DIY for later if you wish. I would change what you mentioned above along with new oil and filter and see how it runs, then take the next step if needed. Good luck and look forward to updates!