Personally myself I would suggest you have atleast 12-pipes. You smoke 4 times a day if I read correctly and with 12-pipes your pipes will have a chance to rest and dry between smokes. So for example take 2-pipes to work to have your 2-smokes and have 2-pipes ready for when you get home to have your 2-smokes. The 2nd day use 4 more pipes to do the same thing as the 1st day, and on the 3rd day 4 more pipes doing the same as you did on the 1st and 2nd day. When the 4th day rolls around use the 4-pipes you used on the 1st day.
This will essencially give your pipes 48-hours to dry and rest between smokes and allow your pipes; including your cobs, to last longer and smoke better.
I don't know what your taste is according to pipes but if you like cobs Missouri Meerschaum makes some very nice cobs for a descent price. If you are more a fan of briar pipes Dr. Grabow makes very descent pipes that are an excellent bargain. Both companies have been around for many years and they have a huge reputation backing them up. I have several Dr. Grabow and Missouri Meerschaum pipes in my modest collection and they are excellent smokers.
But getting back to your situation I think 12-pipes is a good place to start; 2-pipes for work and 2-pipes for home per day, rotate the 4-pipes each day and by the time you get to the 4th day you will be back to the first 4-pipes you started with giving your pipes 48-hours to rest and dry before smoking them again.
Does that make sense?