Here's your questions, with answers:
1. You mentioned using a bar of soap on the "ferrule". Is this the top cap of the sail? If so, I am guesing soap just helps the ferrule slip on-off easier and less likely to scratch the top of the mast?
As Joe WS suggests, the ferrule is the on the top of the lower mast section, and is what sticks up inside the top half of the mast. On some skinny masts, the ferrule actually extends down from the top section.
2. You mentioned wrapping electrical tape around the mast joint. What is the purpose of this....to prevent sand from entering the joint while rigging? Is this something you do even if you are breaking down the mast at the end of every session?
I "re-use" the tape several times. Buy good quality 3M electrical tape (a little pricey, but you can use it more times, and it's peanuts compared to damaging your high carbon mast.
After you apply a little soap (bar of soap here) to the outside of the male part that connects the two parts of the mast (this serves as a lube so it comes apart easy, keeps the close tolerance diameters free to turn when you want to take it apart at the end of the session, and actually seals out sand and salt water to some degree) push the two halves together and turn them relative to each other untl the gap between them closes up. Not all masts are cut truly square to the bore, so if you index them one to another you get the best fit, and maximum strength,
3. So if I am going to upgrade to a higher-carbon mast, does it make sense to go w/ a "skinny" mast? From reading on other forums, a lot of ppl comment that a skinny feels better while gripping the mast. (As a beginner, I will be gripping it quite a bit...) Also, is a skinny "stronger", ie thicker sidewalls. If so, what is the downside of a skinny?
Skinny masts are indeed stronger, but do you want strong..... or lightweight and easy to uphaul.
I use them sometimes, in sails that require them (like my 6.2 m2 Sailworks NX slalom which was
designed on a 430 cm Sailworks Backbone (1.9 Kg.) I have both Sailworks and Powerex Std. Dia. 430 masts (SDM) that weigh less (the Sailworks Joystick 430 weighs 1.7 Kg.,) so I use the mast that the sail was designed to be rigged on in all cases.
Only thing I do not like about Skinny masts is that they all sink due to far less volume of air trapped inside.
It's not so fun to come up from a big wipeout and find you board upside down with the rig pointing straight down toward the bottom.
It's a bit hard to right your board with the mast sunk, and then you have alot more pulling to get the rig up
from pointing down.
If you sail in a shallow place maybe this is not such an issue, but if you sail in water deeper than the length of your mast, ..... beware.
Hope this helps,
P.S All good points made by Joe Windsurfer..... Thanks!