As of January 1st 1997, your car drivers' licence no longer covers you as a provisional licence for a 'learner' motorcycle. Before you can legally ride a motorcycle on a public road you must pass your Compulsory Basic Training (CBT). This is just the same as for modern bikes, as are all other legal requirements. Look in Yellow Pages under "Motorcycle Training" to get full details from a local establishment.
If you passed your bike test many years ago and haven't ridden for some time, don't worry, you're still covered - the new rules apply only to new riders.
Is required - again, exactly as for a modern vehicle. There are certain relaxations of the rules for older vehicles, however. For example, brakes are not expected to be up to modern standards; a speedometer is not required on early machines (I think pre-1936, but check if you need to be sure); lights are not a legal requirement (though if fitted they must work).
Is free, for all vehicles registered prior to 1973. You still need a tax disc, which at least proves that insurance and MoT certificate were valid on the day of issue, but this is free of charge - the vehicle taxation class will be "Historic Vehicle".
Many brokers now offer "classic" insurance at a quite reasonable cost. Check magazines for adverts, or clubs for their own schemes. Cover for multiple machines is generally available at little extra cost, and "agreed value" arrangements mean you don't have to worry about being offered "old banger" compensation of £100 or so if your £3000 pride and joy is written off (a very good reason for NOT insuring old machines on a modern policy).