So I'd like to know: Do your guineas chase and/or kill the chickens?
Not particularly. There's the usual pecking order sort of things: My three adult hens tended to push everyone around, the olive eggers seemed to be on top of the young birds, and the guineas tended to push around the legbars until the last couple months as the pecking order shifted around.
When they had their first spring (around 6-7 months old), they did stress the chickens out with their mating racing / chasing behavior but things sorted out after that. The chickens either flew away or figured out if they squatted the guineas left them alone.
Overall the worst violence has been guinea vs guinea. At about 4 months of age I had guineas bloody each other 4 times (3 of which was the same bird whom I sarcastically nicknamed "lucky" and whom got taken by a coyote two weeks ago after a fallen tree took out part of the fencing on my property).
These days (about 9 months in with most of my mixed flock) the most chasing are two of the guinea males. I'm not sure what the deal is with those two but they'll spend about an hour each day (usually in 2 to three stints) running all over the place. One chases the other, then they switch with some attempted feather pulling every now & then.
Do you free-range your guineas and/or chickens?
Both. I started around 8 weeks with VERY limited outings: one or two hours before dusk, and never the whole flock at once.
After about 4 months I let them out about an hour and a half after sunup until dusk.
Do you have any tips for getting the guineas back into their pen at dusk?
I never had an issue with this. The latest batch of chicks & keets I moved to the coops at two weeks old (it was September and temperatures were mild).
The coops are mosty white (including the polycarbonate roof panels), with motion-sensor activated lights on a 15 second delay so they can find their way in more easily at dusk. My understanding is guineas don't really like to enter dark places so I made the coops as "inviting" as possible to them.
The only issue is the two idiot males that chase each other around. Every once in a while one or both end up on top of the run at dusk and I've got to push them off with a broom and then they go inside on their own.
And, last but not least, how old do the keets have to be to guess their gender by their wattles? I've read that the cocks can have a bigger pair of wattles and helmet than the hens.
I heard at least one of the keets making a "buck-wheat" type of sound today. (Although to me it sounded like "look-alive"!) So I'm guessing that we have at least one female.
The calls are the most reliable way to sex them. A couple of the ones I thought were males based on wattles ended up making the two-syllable call (which to me doesn't sound like words at all but just a sort of "guh-wahk" noise).
I have 13 adult guineas and six of them are female. Mine have a wide range of vocal ability ranging from one that has a very quiet call to one that has a two-tone buzz-saw shriek. The latter bird got very quiet after she paired off (THANK GOD), and a couple never "guh-wahked" that often even when they were looking for mates.