Hi, This is my 1st time answering questions in this forum. I hope I can give you a little more knowledge on your siding project. I do have a couple of question to ask.
1. Are you going to be re-siding your whole house?
2. Are you planning to paint or stain the clapboard?
3. Are you planning to do this project yourself or hire a contractor or siding installer?

As you probably know clapboards do come in many species of wood. In the New England area red cedar clapboards are traditionally the must popular another choice would be eastern white cedar, and eastern white pine. In my opinion all are a good choice. Allot depends on the look your trying to achieve. The application of clapboard are either smooth side out, if you are going to paint or use a solid stain. Rough side out if you are going to use a semi-transparent stain.
With that said you get into sizing and grading of the clapboard. The sizing of clapboard is usually 1/2" x 4", 1/2" x 6", 3/4" x 8" and 1" x 10". The must popular is the 1/2"x6" in New England unless your on Cape Cod, where you will find more 1/2"x4" this size tends to give you more of a old colonial look.
The grading of clapboard especially in western red cedar (wrc)
1.(best) clear vertical grain or (cvg) this product is graded on the smooth face for any defects. The application is generally smooth face out. This would be the best product for painting.
2.(better) A&btr or sometime seen as (aye&better). Like the clear vertical grain clapboards it's graded at the mill on the smooth face but now you get clapboard the will have some vertical grain but also flat grain. This product can be applied smooth face out or rough face out can be painted or stained. I have seen some problems with this grade. If applied smooth face out and painted, there is a possibility of the flat grain raising thus requiring paint more often. Used on the rough side it will take a semi-transparent stain well with the exception of some of the hard flat grain areas.
3. (good)This grade is generally referred to as "Rustics". This product is intended for rough side out application and thus is graded that way from the mill.

So far I have explained species, sizing, and grading/application of clapboard. Let me touch a little bit on the finish.
For the best finish that being how long the paint or stain will last, it is best to back prime the clapboard before installation. When it's being installed it end or the butt of the clapboard should also be primed, but is seldom done because of the extra step the installer takes. But you should insist on this being done as moisture can be drawn into the un-primed joints and resulting in premature failing of the finish. In my opinion the best way to go is with a factory prefinished product. The entire clapboard is primed and a finish coat is then applied. This system generally comes with a warranty. The warranty requirements are struck and must be followed to the tee. The company will provide colored nails as well as the paint or stain to be applied to the butts of the clapboard. The installer needs to make sure to caulk all areas. This is just a sampling of whats available for clapboards. Last but not least if you are hiring a contractor or an installer, get 3 quotes on the job. Put everything in writing and make sure to check references. Do your homework well and you will end up will a fine job. I also added a link which is the Western Red Cedar Lumber Association which has good information as well as links to other articles.
Good Luck Greg
ps I am not a buisness but was involved in the building material buisness for 25 years before retiring.

Here is a link that might be useful: western red cedar lumber association

Thank you so much for all the very helpful info and for the link, also helpful. I'm sorry not to have thanked you earlier--was on vacation.

Your questions:

We're doing one side only at this time but it is three stories high. It will be painted. A contractor will be doing the work. We're changing the windows too. We'll do the other sides as needed.

This side faces east which means it gets the strongest horizontal rays of the sun and thus has always required more maintenance. I really appreciate your tip about painting the cut ends of the siding--great idea.

We are getting pre-primed siding but not pre-painted--didn't know that was an option. I'd like to keep the same color of the house now so I don't think pre-painted will work for me. Besides, it has to match the three sides we're not doing yet.

Any more ideas are very welcome. We're ordering the material very soon for mid-September installation.

Three words that will extend the life of your siding, finish, and maintanance schedule.

Vented rain screen.

OK, I give up--what's that?

What rollie is talking about, i believe, is running vertical furring strips on the exterior wall so that there will be an air space between the wall and the siding.The furring strips are generally acting the same as the wall studs at 16" o.c. You also have to frame around openings at the perimeters.The theory is that by having the air space,moisture is allowed to run down and out at the base of the starter piece and not collect between the siding and wall when nailed up tight to the exterior wall.It's an extreme application imo and a bit overkill, as my days on cape cod i witnessed cedar clapboard sidings that were in remarkable condition on 1700 era period homes. The use of a good underlayment between the siding and wall as well as proper flashings is key along with a very important fact that greg mentioned: when they make cuts, prime the cut ends before hanging as well as back priming.We had a couple of carpenters help us with the facia and soffits on our build and it was the first time i ever saw a carpenter keeping a paint brush within reach to stain(in our case)the cut ends before hanging as well as for touch up.Rollies suggestion is great and definetly solves moisture concerns. You have to keep in mind the extra 3/4" being furred out means special trim methods around openings.Ask your contractor their take on the furring method.