Hello!
When you get an aruba instant you dont need any controller
It can work as a stand alone or work with other instant which means that for example
Let say that in your office you cannot cover it all with one IAP 205 and you need 3 IAP 205. If you put them in the same network they will form a virtual controller in which you can control all of them with one virtual console.
You dont need any license the aruba instant brings all the license for free. So you got the firewall capacibilities already on it.
Being said that
Now lets go with your problem. It seems you have got a lot of interference in your office. Your issue is that 2.4ghz band just got 3 usable channel. And it seems that in your small office you can see around 30 aps in the same band, which is bad. You are all fighting 3 channels...
Now it could be a noise issue which is bothering besides the interference. I have been in situation in which 2.4ghz band is no usable for interference and noise at the same time, but 5ghz band its good.
I would advice you getting 5 ghz capable devices(laptops, tablets,etc) if you already dont have those... in 5ghz you got 23 non overlapping channels vs 2.4ghz that just got 3 non overlapping channels.(as a personal thing all wifi devices i buy must run in 5ghz, dont really buy devices that just work on 2.4ghz)
Having your devices that works on 5ghz you should be able to have a cleaner channel and a good wifi.
It would be good if you had a arubanetworks partners near your area which can give you a demo for a week, at least we do that. The client try and most of the times buy. If you got any trouble with 2.4ghz the engineer should be able to see it and advice you on what to do.(hopefully you will get a good wifi engineer)
I really dont know if you are a techy guy and i hope i didnt confuse you with what i tried to explain you. As you sounds like you are like the owner of the office and you just looking for something to work in your bussiness :)
Cheers
Carlos