I couldnt help but read through the topic. I am 25 and have been sailing since I was 14 so I am sure to some I am still considered a minor here. But I used to deckhand and be second in command on a Swan 46 "Dakota" for racing and cruising. Going up the mast was always my job due to my weight and limberness.
We first off never used a wooden chair, they do not secure you enough. I went with a nylon style chair that had a harness clip in the front and wrapped around back. The other style is the climbing harness which straps around your legs and waist kinda like climbing gear so you can monkey around up top.
Anyways he had a 65 foot mast so going up for me was fun. A double set of spreads and B&R rod rigging. Well going up be sure to do this first, take your halyard and loop it through the U-hook or whatever you have as the attachment point, tie a bowline then bring the actual halyard clasp down to the attachment point and secure. This way you have a nice secure setup, if the clasp lets go you are still on by the know and vice versa, good to have a backup. All heavy tools should be tied on by small lanyards, I used clips at the end for easy access.
When going up the rigging you should have one if not two men down low. I went with two, one to hoise you up faster than just cranking a winch and the other to tail the winch and crank. When being lifted help the guys out by using your feet to push you away from the mast and walk up it. This gives them better leverage to pull and you better access to climb. Do not stand on the spreaders and when going up or down always look in the direction you are going to be sure you are free of obstacles or snags. Continuously check your line and where it is so you are not wrapped around anything above.
Once in your work spot have the person or people down below keep the line secured around the winch and the self tailer if you have one and then have the line cleated off as well, again a double secure. Typical reasons to head up a mast are generally taping the spreader wingtips and checking and lubricating the top of the mast and lights as well. I use Sailkote on the pulleys, sail tracks and only tape, not those rubber boot tips for the spreaders, they cause more friction on the sail than tape.
I used to go up during races as well to free or retrieve halyards and sails and such. This I used the climbing harness to allow more mobility, especially when the boat is heeled over and your doing 8-10 knots (remember it was a Swan 46, big boat) offshore. That is when you can climb around lift yourself up and really feel the stresses on the boat such as the shrouds.
I would also not recommend going up the mast while the boat is on chaulks. The boat should be secured enough for working on but once up the mast even if you only weight 150lbs. that weight is increased the higher you go so the center of gravity can be changed. I would only recommend going up while in dry dock if you are going straight up and down along the mast, not off to the edges of the spreaders.