Most things were well answered indeed! The sharpie will be a very big help to help you get your angles correct. You want to ware it off so the clean patch JUST reaches the edge. To get started, pick up a mixed grit pack of the black wet/dry sandpaper. Places that sell DIY auto body repair supplies will carry mixed grit packs and from there you just replace what you use up.
To cover your points:
1) Pressure is the key part of all this. As light as you possibly can without having the blade wobble, or "stutter" across the paper. Light, smooth, slow passes. As you reach the end of the paper, do a full stop, THEN lift the blade up. Going off the end or lifting during the pass more often than not changes the angle to a much steeper one that won't get very sharp. The hardest thing is fighting the urge to press down thinking the abrasive will cut the steel faster. If you want more aggressive removal, drop to a coarser grit.
2) As far as grits go, 800 is a good start, but the honest truth that I have found is that steel type, heat treat, and even blade geometry will all affect how the abrasive performs. 800 is a safe starting point in that it's scratch pattern isn't overly aggressive, but not so fine as to just polish without reforming the edge. Some stainless steels and super steels you may need to start as low as 400, others starting at 1000 may be plenty aggressive. I keep grits in 400, 600, 800, 1000, 1200, and 1600/2000 on hand. Usually, increases of 400 is a good progression.
3) When to change grits. Each grit has its own scratch pattern. The first thing to check is that you have completely and evenly covered the contact area of the blade with consistent looking scratches. Once you have that, check to see what the edge feels like either with the touch of your finger tips (carefully!!), a paper cut test, or whatever guide for "sharp" you normally use. Increasing grit is refining the edge you got from the previous grit, so even at 400, you should be able to get a sharp but very toothy edge. Move up a grit and once the finer scratch pattern has replaced the rougher, re-check your edge, and if you are happy, move to a finer grit until you get that edge as refined as you want. Eventually, you will be doing almost zero removal, and all polish if you take the grits that far. Just be aware that some materials cut better with a slightly toothy edge, than a full polish. Also, some steels (like D2 for example) perform better if left a bit toothy, and retain the edge longer. My first experience with D2 was that it actually got duller if I tried anything finer than 1000 grit.
4) The rule of the number of required passes per coarseness of grit really leans to you may be using too fine a grit for the amount of removal/refinement you are at in your progression. There may be more passes as you move through finer grits, but it shouldn't be much more than roughly 20% per grit increase, tops. If it seems more than that is needed, consider dropping down to the next coarsest grit for a few passes, then going back. Many straight razor guys swear that switching back and forth between 2 grits (eg: 20 passes@800 +5 passes @ 1200, 15@800 + 10@1200, etc etc until you drop the 800 completely) is essential to their razor honing. I've used it when one grit is pretty worn so I'll use the next grit finer instead. It's not a rule, but if you are having difficulty with a blade, it may be worth a try.
5) stropping can indeed remove the last of the burr. It's really about refining the edge and smoothing out the tiny imperfections left by honing. Including, but not limited to the burr. I use a wine bottle cork and drag the edge across it a couple times whenever I change grits. It removes the rattiest parts of the burr, and some of the metal and grit particles very nicely. It does (it seems to me) a couple things: first, it cleans off the edge on the cork, not your paper. You get a more true feel for what the paper is doing right away, and not go through a few clean-up passes. Less passes, and less deposit means your paper will last longer. The other thing it does is give you a more honest feel for where your edge is really at in your sharpening regiment. It removes the tiny wires and such that might feel very sharp, but really have nothing to do with the edge you have created.
6) stropping. Stropping is in basic principal the same as honing, in that the abrasivness of the surface removes metal at a certain rate. It is the last steps in evening out the edge and removing the last imperfections as well as "combing" the microscopic strands and irregularities into a smoother edge. This is the fine tuning stage. Grits on strops differ from every other abrasive, whether it is sand paper, stones, ceramics, or diamond sharpeners because the grit itself can move on the strop surface. It has more give, and is more "gentle" than the same grit in a fixed media, while still offering a similar scratch pattern. The way I see it, fixed media tells the steel what it is going to do, where as with stropping, the steel tells the grit what it needs. A fixed particle is going to scratch the same way every time steel passes over it. A moving particle adjusts based on the shapes of the irregularities that pass over it, plus the up-and-down as well as side-to-side movement of the leather fibers. As to grits, plain leather is 100% pure polish, with minimal removal, at least until it gets abrasive grit, and metal particles in it. Then, it is a bit of an unknown as you really have no idea what particles are in it, what the functional "grit" is, etc. Using compounds or pastes traps the grit in the oils, waxes, pastes, etc, and minimizes its effect while offering a more consistent abrasive or polish surface with its own grits. Straight leather basically cleans off the blade, compounds refine it. They also make the strop work faster. If you are considering using compounds, go with the coarse or medium like the black and green bars, or 1 micron and .5 micron if you spring for the pastes. Going finer and getting the most out of it requires more skill, and functionally is really just bragging rights as far as real world performance gain goes. Unless you shave with your knife all the time, you would be very hard pressed to notice any difference in cutting improvement or edge retention, when using fine or ultra-fine stropping grits. Having said that, stropping is what turns a blade from very sharp to scary sharp, and is a great way to quickly touch up a blade so that full honing doesn't have to be done nearly as often.
Sorry for the LONG post folks, I learned of convexing and sand paper a couple years ago, and went through a lot of trial and error based on snippets of information here and there. The learning curve can be very frustrating at first!
MODERATORS: there is an excellent video tutorial on a knife vendor's web site on convex/sandpaper sharpening that I would like to put a link to, but I'm not sure if that violates a forum rule for promoting a business or such. The videos themselves do not reference or promote any specific brand, vendor, or product, but being a commercial site, I'm not sure if linking would be viewed as advertising. Please email me if you would like to see the links, and judge them for yourselves.
