I wish your event were happening out my way... I'd be happy to loan you a system for the day! Hopefully you'll find enough supportive musicians in the area that you might not need to buy or rent anything this time around. If you do buy something, try to aim for quality gear for the long term. Better to spend a little more one time for something good than the alternative.
MIXER
Congrats on scoring the Allen Heath mixer. It's clean sounding, simple to operate, and has swept mids. The digital effects are decent, though a dedicated outboard effects processor is noticably better than what is included in most compact mixers. If a guitar player's sound requires sophisticated effects, they'll probably bring their own preferred effects units with them.
STANDS
I second the vote for K & K mic stands. Absolutely worth it long term and a joy to use. Please do NOT go for the cheap ON STAGE mic stands and speaker stands. They're bordeline when new and only get worse with time.
SPEAKERS
All of the speakers mentioned will have plenty of volume for this small of an event, with the possible exception of the Bose. But the claimed number of watts and dB and marketing hype specs don't begin to tell the whole story on sound quality. Same way an entry level Recording King guitar might have similar "specs" to a vintage Martin or custom Froggy Bottom guitar, but they sure don't sound the same! If you're willing to invest in long term main speakers, another one to consider is the RCF HD 32-A MK4. It's an exceptional speaker in its price range for acoustic music. The compression driver on this is unlike anything else in its class. If going more budget, might consider the RCF HD10-A MK4 or ART 710-A MK4.
While you usually see a speaker on each side of a performer, I agree with the poster who said for this event, you might do fine with a single speaker, placed a bit behind the performer and up high, maybe around 10 feet up and angled downward at the audience. Most speakers send out their most balanced sound in a "wedge" shape, often about 60 degrees vertical and 90 degrees horizontal. Outside that wedge, the sound is more muffled. So depending on the seating arrangement, and distance to the speaker, you might get fine coverage with just one speaker. Assuming it's a solo performer, at moderate volume, and you're running things in mono.
MICS & WINDSCREENS
As for microphones, the list is long. The already mentioned Shure SM-57 (and Beta 57-A) can sound quite good. Moving up to a condensor, an Audio-Technica Artist Elite AE5100 sounds wonderful on acoustic guitar. Careful placement (and judicious EQ) counts for a lot. Different guitars have different sweet spots. Experiment during a sound check if possible. 6 inches away from where the neck joins the body is a good starting place for a single mic. Try not to aim a mic at the sound hole. Use duct tape when necessary to keep moving guitar players in place.
Proper fitting windscreens are vital for outdoor use. Mics pick up even a slight breeze (and amplify the heck out of it). In my experience, some of the thicker proprietary microphone windscreens are worth the premium price over generic covers.
Good Luck with the event! If you want to chat about more ideas, PM me with your phone.