Im looking to buy a 650 single dual sport but was also considering a little larger cc adv bike. Is a twin cylinder a lot more difficult to work on for a beginner? Or is it all the same as a single besides the other cylinder?
IMO, it depends on how the fuel is delivered to the engine. If it has carburetors, two or more carbs will require that they be synchronized, otherwise, you can do just about any other required adjustments for each cylinder, whether one or six. If you are a beginner, you may want to find out if the valves have adjustments, or are self adjusting. Most (if not all) newer bikes have some form of electronic ignition, so unless you go vintage, there should be no adjustments there, just replacement spark plug(s). I find the most important tool for any machine is a good service manual; finding one for your selections should provide you with what kind of maintenance you will need to learn - you can skip the sections on tear down and rebuilding, but those sections may have some tips on the maintenance procedures.
I never thought I wanted a single until I started riding one and now I really enjoy it, the simplicity, the vibration, the distinct thumps of the exhaust note as I motor along. I feel like I can almost count each power stroke.
One thing I noticed, when things go amiss on a single, it's easy to diagnose. There's no confusion about which spark plug is misfiring, which cylinder is running lean, or which carb is acting up. There's no chance that the poor performance of one cylinder will be masked by another running right. But there's also no chance of limping home, you are pushing.
I like twins too. More than two cylinders on a motorcycle to me seems gratuitous.