G'Day Derek,
Re Climbing the mast;
I use ascenders like maintaineers use. See the A1 811 from this site;
http://www.srte.com.au/ascenders.htm.
I am not trying to plug them. I climb up the spinnaker halyard with the ascenders. One ascender is attached to the top of the bosuns char. One ascender is attached to two stirrups that your feet sit in. It is a simple matter of standup, sit down to go up. The genoa halyard is attached to the top of the bosuns chair as well.
Coming down, the ascenders are released but not taken off the rope. You keep them open with your fingers only. Another crew lowers you down on the genoa halyard. You must be in front of the mast. If you wanted to use the main halyard you would have to be behind the mast. If you have snapshackels don;t trust them and shackel directly to the eye on the halyard.
Take a lanyard up with you that is attached to a bucket so that you can haul up or lower bits to the deck. Saves coming up and down the mast. The crew on the deck has no load.
My wife usually controls the genoa halyard. How is that for trust !
All the climbing effort is taken by the person climbing the mast in the stand up sit down method.
I use a second halyard as I once was winched up a moored trailer boats mast and 3 months later the halyard broke as it was rusted at the wire to rope splice. In hindsight we should have noticed the rust at the joint. Its always nice to have a backup.
Inner forestays;
I've sailed on two boats that have lost 3 masts. The first was lost because the mast was pumping when working into a SE chop off Sydney. An inner forestay would have stopped that. My boat has fore and aft lowers so it is pretty stiff, don;t know about other Top hats? The second boat had a "Baby Stay" that is only used in choppy conditions.
Felicite is a mast head rig.
I hope that helps and its definitely not too many questions. Im sure others will fill in the blanks and have different opinions.
Greg.