Concerning oil filters, this link, http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilters.html, is a great resource.
Concerning synthetic oil, what else can be said that gserep1 didn't already say in his excellent overview? There really is no question that synthetic oil performs much better than conventional petroleum oil. Why not spend a few extra bucks and ensure that our high-revving engines have the greatest level of protection possible? And with the extended drain intervals that synthetic oil provides, the additional cost is mostly negated.
If you would like to see some more proof, please go to: http://www.mobil1.com and see what the experts have to say. Either 5W-30 or 0W-30 would be excellent for your car katraak, and would give you great gas mileage to boot. These oils will provide great protective qualities. I would lean more toward 0W-30 if you travel in snowy weather for awhile. These oils flow at 50 below 0 for the 5W-30, and 62 below zero for the 0W-30, so cold weather performance is no problem. Mobil 1 has just reformulated their oil again and they now call it "tri-synthetic" because they have added a 3rd ingredient into the puzzle. If you have the time, please read the website..especially the part that says "Why synthetics?". You will begin to understand how good this stuff really is (synthetics).
Also try the part that talks about myths about synthetic oil. This will also help a lot. For myself and mayankhp, we can get by with 5W-30 synthetic. I am not sure where "zhz" is from, but one of these two oils should be fine. I have had such good luck with the 0W-30 in the Explorer, it will be a hard decision to figure out which one to try first. We can't go wrong either way.
I would like to recommend another product to use on the Sentra. That is a K&N air filter. This unique filter will replace the paper one in the car with a cotton filter reinforced with a mesh screen on both sides of the cotton for added stability and strength. This cotton is oiled with special K&N oil that causes dirt to cling to the filter and not get into the engine. This will keep your intake manifold cleaner, and thus keeps dirt out of your oil. It is cleaned generally once every 50,000 miles, but I clean it a bit more often due to dusty conditions I drive in. It is fully washable, and can be re-oiled and left to dry before re-installing.
This filter has a 1 million mile warranty, and is truly the LAST filter you will ever have to buy. I have one in every vehicle I own now, and this goes back to 1987. They are a favorite of dune buggy and dirt bike racers worldwide, and if they work for them, then they will work for us.
You can go to: http://www.knfilters.com and see for yourself. All 2000 and 2001 Sentras need K&N air filter number 33-2031-2. It will cost from 30 to 40 bucks, but it will not have to ever be replaced again, AND it flows better DIRTY than ANY brand NEW paper filter. It is cheaper to buy these filters through a distributor, like pep boys or Autozone instead of on line, because the company gives monetary incentives to distributors to sell their products, so they pass it to us. Good deal all around. They keep the intake manifold cleaner, and thus keeps the engine oil cleaner as well by blocking so much dirt.
I guess that I had better go now, and see if I can find this air filter, or at least get it ordered. I changed my oil at 3000 miles and used Castrol GTX 10W30 yesterday. I put in 31/2 quarts, and I hope to have this in until 9000 miles are reached. The oil was a little dirty, but not black, by any stretch of the imagination. The car starts up, and the valve train noise is nearly totally gone. I am sure that synthetic oil will help this a lot.
Have fun, and don't forget to write when you can!