Re: Going up the mast
When you go up the mast, make sure that the on deck crew are not directly below you. If the halyard winch is on the mast, rig a block to lead the halyard back to another winch. Rig the second safety line away from the mast too. Even if you think that you have lanyards on everything, there is a risk that a tool or the parts you are working on will drop (not to mention the risk that you will drop if any of the hardware fails). You don't want your on-deck crew hit by any falling objects. They won't be able to lower you back to the deck if they are unconscious.
If you go up at the dock on a calm day, you probably won't need a tether to the mast, but if you go up while at sea, I would definitely tether to the mast. If it were really rough, I'd consider two tethers, so you can fasten the second one above the spreaders before you have to release the first one from below the spreaders.
I'd prefer to rely on a knot I tied myself than a halyard shackle to fasten the climbing harness to the halyard. (If I'm gonna die, I'd rather know who messed up the connection.) Brion Toss recommends a buntline hitch. But a bowline will hold as securely, and with a climbing harness you shouldn't have a problem with the extra length of the bowline compared to the buntline hitch. (The bosun's chair attaches to the halyard about even with your neck, and if you tie a bowline, it's harder to hoist the end of the halyard high enough to get your head above the top of the mast.)
Also, no matter how hot it is the day you go up, wear long pants. A cotter pin can make a nasty laceration when you are sliding past the spreaders.
With a little planning, a trip to the top of the mast can be very manageable. Have fun and enjoy the view.
New Orleans, LA