I stayed at the Matoula Appartments just over a week ago for 1 week from 16th June to the 23rd June.
When I first walked into the Studio Appartment it looked pretty basic but very good for greek standards.
It had 2 beds close together.
a kitchen with a cooker,sink and fridge and a few cupboards with plates etc in.
To the side of the kitchen was a bathroom with a shower and toilet.
In the main room where the 2 beds are there is a tv with a few sky programmes.(2 music channels,euro news,world news and a documentary channel)
There was also Air conditioning in the room but you have to pay for it at the main reception which costs 4 euros for 24 hours.Its well worth it.
With you going in September you may more than likely not need the air conditioning as it can get quite cool at night time.
The weather at that time of year is normally pretty good but you may get an odd shower or 2 while you are there.
There is plenty to do in Acharavi but if its too quiet for you the next resort Roda which is about a mile away is more livelier.
Most things are quite cheap in Acharavi.There is a supermarket just up the road from Matoula Appartments and main meals in Taverna's cost around 7 to 8 euro's.
Am not sure what the mosquitos will be like in september, but we noticed in June that we are more bothered by the mosquitos, and were bitten alot more than usual.Since coming back home someone has reccommended using "Boots" Insect repellent (Tropical) in grey bottle that contains 50% DEET. This is supposed to be very effective and will keep the mosquitos at bay.
Any other question that you need answering about Matoula Appartments or Acharvi itself then don't hesitate to contact me as I have a good knowledge of Acharavi with going quite a few times.
Hope this information helps and answers your questions
I have also sent this message to the message board on the forum for you to read and to help others if need be.