Mind your fingers if you are carving a pipe bowl. It is easy to slip and I have some very deep cuts in my left index finger from doing exactly that.
I have found that if you want a quick pipe stem the best thing to use is ordinary garden cane (bamboo). Simply saw a section outside of the notches, bore through where the plant closes off each section inside and push through a piece of coathanger wire of something similar to remove the soft tissue in between the sections. You will find the saw and awl on an SAK perfect tools fo this.
Other tips:
If you are carving a bowl and attaching a stem make a stub on the bowl for the stem to go into and make it longer than you think you need to, that way when you attach the stem if you are using glue the heat from the bowl won't destroy the glue.
You may want to angle the hole into the bowl that the stem fits into so that you can see the tobacco. This makes lighting the pipe and keeping it going a lot easier.
The best way to keep the stem in place is with a deep friction fit into the bowl as it will easily allow you to take it apart and clean or refit a stem. If you are going to use glue you will need to use a good 2 part epoxy clay. Milliput is good for this if you can find it, it has a high temperature tollerance.
Again, if using glue, and I suggest you don't, at no point should the glue be exposed to the smoke. You do not want fumes in the smoke.
Wait until you have the pipe constructed completely before treating the wood with anything.
Use well seasoned wood for your bowl - if it is even slightly green it will begin to crack the first time you light it and it will just get worse. Don't be afraid to leave the bowl walls thick. This gives the bowl better heat resistence and longevity as well as a nice weight, you can also carve patterns on the outside!
You can lightly treat the inside of the bowl with corn (maize) oil a few days before you do the first burn. This is a high temperature cooking oil and will get well into the wood and 'cook' it so that it chars and protects itself from burning too quickly.
Don't smoke the first burn of the pipe like you normally would. Woodsmoke might smell great but it doesn't taste too great, particularly if you've oiled the bowl!
Aromatic tobacco is best in homemade pipes - cherry or apple is lovely.
As final note, if you make anything that looks 'different', it's best to be with understanding company when you smoke it. Our friends in blue often take an interest in peculiar looking pipes and passers will be wondering if you are some kind of wood-elf!