What about these snakes is it that makes them harder than others to keep?
Arboreal animals tend to be far more instinctualy set in their behavioral patterns and environmental needs... This is a tendency, not an absolute but- they do stress a bit easier than terrestrial animals, it's fairly easy to simulate some dirt and leaf litter, far more difficult to simulate a tree twenty or more feet off the ground. Both in terms of the instinctual need to be "Up" as well as the environmental conditions that exist (temp, humidity). A terrestrial animal will get rained on from time to time and will become Wet. A strict arboreal species needs the proper humidity but will experience problems with an enclosure that is simply "Wet", the animal does tend to attempt to get higher than you're usually willing to build an enclosure and; behaviorally, the only organisms they encounter are predators (and they have limited options for dealing with that), Prey (which is usually somewhat less frequent than that found on the ground so they react quickly when not stressed or ill) or occasionally something to mate with, this tends to alter their actions to a strong degree when compared to some of the more popular and common species.
Most arboreals tend to more aggressive than most terrestrial snakes. I hesitate to categorize this as a serious problem because there are a few ways that it can be easily dealt with and they don't need to be handled anyway but it is something many neophyte keepers take issue with... and yes, the teeth tend to be large (and are in the two species you named).
I wouldn't really call any of these things significant barriers in their captive care and I would say that the animals are well within the realm of anyone who's willing to take some time when setting up an enclosure and do a bit of research into the animal's biology and behavior (as you obviously are). Some experience with proper manipulation of environmental conditions is helpful.
What should a newbie know going into keeping either of these species?
Start with an adult that's either very well established or captive bred and comes with detailed feeding/shed records.
Buy from a reputable dealer even if it's a bit more expensive for your first shot.
Arboreals tend to have a stronger nocturnal feeding response than many other species and stubborn feeders will usually react well to scented or alternative prey items when the environment is correct.
Those teeth do hurt a bit and they will use them. Approaching the animals properly in well lit environments will lower these tendencies to a great degree but the proper approach is something you need to get a feel for, it can't really be written out and learned. It really doesn't hurt
that much in the grand scheme of things, I've stubbed my toe or bumped a funny bone and been in much more pain.
Take your time with your first animal and invest a bit more in the environment. This investment doesn't have to be additional money but a bit of forethought and time will save a lot of potential problems.
How much hands-on general experience do you believe a person should have with snakes before keeping either of these species?
Exactly two years, four months, sixteen days, ten hours and eleven minutes, heh.
It's not something that can be pinpointed, it's really a matter of personal aptitude combined with experience. These animals aren't established corn snakes by any means but they're not as difficult as a lot of popular texts will make them out to be. If you look at the requirements, do a bit of reading on the natural history and behavior and think you can do it, go for it.
My personal recommendation is the Chondros by the way. They have a reputation for being a bit more delicate but they are also smaller by a good measure (and better looking).
I know that didn't really answer too many specifics but if you have further, more detailed or specific questions, I'm sure somebody will answer them.
