A few things to add re varroah for those who haven't read (and should have!) all the relevant material.
Defra PB10859 Managing Varroah is an excellent booklet on the subject. Facts and does not pull punches or extoll the virtues of any particular method.
Mine is far outdated, probably, at June 2005 and updated reprints are probably fairly regular occurencies. Everyone should have one.
Simple. Monitoring and taking effective appropriate action early is the key to success.
By all means, do your own thing re-control - OA, thymol, formic acid, lactic acid, apiguard, brood trapping/disposal, icing sugar, talcum powder, frame traps, drone brood removal, open mesh floors, other systems.
To be on top of it all the time, use, or have available, several of the methods as appropriate. Remember the times that maximum knock-down is achieved (at times of no sealed brood, normally), the most effective for the time of the year, inappropriate methods ('cides' and chemicals with respect to honey flows) at different times of the year.
There is nearly always a method available to suit the conditions providing it is not an emergency situation to prevent total colony breakdown occurring imminently.
Varroah will destroy your colony, given the opportunity. They are a parasite and do not live symbiotically with your bees. Yes, there are some colonies which can resist the effects of the mite, by controlling their numbers, and these are being investigated but until you are prepared to risk a colony, give them some help, well, all the help they need.
That means monitoring, monitoring, monitoring. And action at the first confirmed signs of excessive or potential excessive mite numbers. Beginners beware, especially.
Regards, RAB