When I did the front end of my motor while I had it out, I replaced the water pump, tensioner/pulley, and idler. I also replaced crank and cam seals but the cam seals were more trouble than they were worth replacing them. . I was given the wrong type of seal from O'Reillys and had to replace them again but unfortunately after the engine was already installed (intake cam very hard to get to). I say this because these seals IMO fall in the category of "If it ain't broke, don't fix it".
If you buy a kit w/ a tensioner/pulley from RockAuto or anywhere really and use all the parts in it, keep an eye on the belt after the installation (you'll need to leave the top belt cover off). Reason why I recommend this is because I had a bent arm (thingy the actual tensioner pushes against) and this caused the belt to pull inward toward the motor which was shaving the belt away slowly. Had it have not been for the clear cover, I would have driven till total failure.
This issue was not only frustrating but cost me more money because I had to buy another higher quality belt since I didn't want to use the supplied no-name belt supplied with the kit. On top of that I obviously had to replace the tensioner/pulley assembly so in the end I only used a few parts from the kit. If I did it over again, I'd buy individual parts based off my preference, may be more expensive that way but in my case it would have saved me a tremendous amount of time and frustration. . as well as money. This was all a kick in the nuts because I had to redo everything but the clutch install (Thankfully! ! !) with the engine installed due to incorrect/defective parts.
Anyways, good luck! Hope yours goes smoother than mine