Speaking from personal experience... even roosting in the trees within a well fenced piece of property they are still potential predator bait. Owls are a huge problem for Guineas, as are other night time predators that can scale fences and climb trees. Unless you are prepared to lose some or all of your birds, I'd avoid letting them roost in the trees if you have other options. Once a predator knows there is an easy meal on your land, they tend to keep returning until the food resource is depleted.
Once the Guineas learn to fly up, and make it a habit (like to roost in the trees for example) you can pretty much count on it that your 6 foot fence will not exist to them. Guineas can be trained to respect fences tho. I have a breeding flock of 20+ Guineas that I pen raised, and they are allowed to free range my goat pasture during the day. They reliably come in at night and their roosts are no higher than 5 1/2 feet tall. They have never roosted in the trees and they don't even fly into the trees while out free ranging. They do get feisty/cocky at times and get up on top of their covered pen and the goat shed and give everyone down below heck, but for the most part they are "Ground Guineas" lol and stay out of the trees. I have never clipped their wings, I haven't had to. They have learned to respect my 4 foot tall pasture fence and stay within the pasture, for the most part. I do have to go herd one or 2 back in on occasion but usually they see me coming and jump/fly back into the pasture, they know the drill. I do not let them free range when I am not home, only when I am able to check on them from time to time. This is most likely not the typical case with everyone else's Guineas and Guinea experiences, but it is a personal success of my own that I achieved thru persistent training and correction... and it took about 5 months to get them to this point (once I gradually started letting them free range at 4 months old).
A small flock of Guineas co-mingled in the same coop/run with other poultry doesn't seem to work out too well for most people, especially later on after the Guineas have matured and breeding season begins.... so a separate coop/run for them would probably be your best choice, (some do attain perfect harmony tho, it's not an impossible task). And personally if you go thru all the trouble of building them their own coop, I'd want to train them to go in at dark and be locked up safe in it every night, (but out free ranging my yard/property every day). You mentioned you have a large pen for your chickens, but you didn't say if you let them free range your 1 acre or if you planned on letting them all free range together... but obviously if you do not let the chickens free range with the Guineas at the same time, then you should not have the aggression problems others experience with the not so perfect male to female ratio, whatever that may be. There is no perfect number
for everyone, it of course varies depending on everyone's individual coop/run/free range/additional poultry situation differences. The 1:5 ratio does however does pretty accurately apply to the amount of Hens one male can cover (fertilize), altho I have had 1 male cover 10 Hens recently, pretty consistently. IMO (and this is just my personal opinion based on personal experiences with both small and large flocks), the male to female ratio is really only a substantial concern when you are co-mingling them with other types of poultry... a flock of only 6 guineas (if raised together, but kept separate from other poultry), no matter what sex ratio will work out their own pecking order, and you may or may not end up with a low bird that gets picked on and rejected by the others. And of course the more room in the coop the better when it comes to Guineas, for a multitude of reasons no matter how many Guineas you have.
As far as sexing keets... the Buff Dundotte and Buffs can pretty reliably be sexed by the lighter and darker shades, so can several of the other Guinea colors in the tan family (Hens are usually darker). The rest are impossible to sex until the Hens start making the 2 syllable call at around 5-6 weeks at the earliest.
Sorry for the long winded post... lol, hopefully I answered all your questions with enough info to provide a broad perspective of what you are headed into
