My bike has been in storage for around 3 years. I will be changing oil and oil filter before I start it up. I will also be cleaning the carb of old petrol.

What else should I do before I try to start it up? My concern is that the cylinders would be dry. Someone suggested that I spray a but of Q20 in the plug holes before I start it. Would this be a good or bad idea?

Would it be better to turn the motor over by hand a few times instead?

If you are going to put oil down the plug holes then you may as well turn it over by hand while they are all out. It's easier. Lol

So turning over by hand will lube the cylinders enough?

Change the oil first - so its new oil in the engine. Pull the plugs. I'd spray a VERY LITTLE WD40 down the cylinders & then rotate it few turns - NOT FIFTY !
REPLACE THE PLUGS with NEW ones - NOT FROM EBAY !!!...
These little bikes hate spark plugs & if you are going to pull them then replace them - the old set can be spares.

I would probably then try & run it from a fuel bottle with NEW FUEL plugged into the carbs.

It will be smokey for a minute until it all burns off ..

Perfect, thanks. I will do it like this.