On your Sentra you didn't say how old the current clutch is. If is original to the car you should replace it while everything is apart. Courtesy Nissan (they have a website to look at but you can also call) sells a nice set-up with an upgraded ACT pressure plate and a stock late model SE-R disk (which I beleive is carbon-kevlar friction material). This set-up with a new throw out bearing should last a very, very long time without too heavy pedal effort.

The best radiator is the Nissan Motorsports HD radiator, which is really the euro market turbo 20DET part. This also includes a higher pressure rad cap (same as a turbo Z cap). With this rad you will not overheat and may need to cover some of it when outside temps are very cold. If you do not upgrade, a new stock type part with a higher pressure cap would be far better than an old partially clogged up part.

The Stanza pulley is supposed to be a good set-up to lower the water pump speed. I think non-AC equiped Sentra SE-Rs also had a smaller WP pulley as stock. You will also need a slightly shorter polyrib belt for these pulleys. The underdrive crank pulley as already noted does not have a harmonic balancer. On the other hand it will slow down both the water pump and the power steering pump. Again I would talk to the guys at Courtesy Nissan.