1- Tubes: Do you patch them or throw them away and use new ones?
Always Patch At what point do you throw them away if you patch them? Up to 4 times then toss it
2- Do you ever buy the tubes in bulk?
Just buy a few when they go on sale. My local trek store has them buy 2 get 1 free about twice a year along with a coupon for a free coupon twice a year
3- CO2 inflating heads: do they make any with a psi gauge?
I carry a small pump that also has Co2(lezyne Road Drive CFH). Use the pump most of the time and only have the CO2 for when I am in a hurry. I blew mine off the bead today.
4- For the tires, do you ever swap the front and back to even out the wear?
With the last pair, I swapped front to rear at about 1000 miles (when I had to change a tube anyway) And at what point to do throw the tire away and get a new one?
I run them until my wife see the tread peeling and starts asking about my life insurance policy I run gatorskins and my pair has around 1700 miles on them so far. Wondering if I should get a new back one or swap out the front and back.
Got about 2400 miles out of my most recent gatorskins, keeping in mind I am not a little fellow 