Simple (ish) encoder and rotary advice

Hi. Im about to try to expand my very basic sim. At the moment, I have TH2Go with 2x22" monitors, and 2x22"monitors "spare" that display Plan G, Teamspeak etc. I fly exclusively GA generally to a very poor standard, but I enjoy it.
I have Saitek everything, X52, yoke, throttle, pedals and, also Radio, Multi and switch panels. Having seen some of the posts on here, I have decided to make an overlay for one of my spare monitors to display gauges. I intend to run this on my spare i5 2500k PC.
So, what I need to find out and clarify is what is the best way to achieve this. I have read about rotary switches on here but am confused as to whats the most cost effective way to use them. The multipanel has all the functions that I need, but I would like to have a knob to turn for the heading bug etc. Also, any general tips on where to start with this would be greatfully received. I live in UK, so suggestions for any UK centric resources would be handy too.