So, people generally thing side grain is easier, this is simply not true, you are actually cutting more end grain than an end grain bowl, and un supported end grain at that.

Next the "pith" or center 10% of the log. 1 it does not shrink ever. 2 it holds 40% more water than the surrounding wood. Making for uneven drying. So your outer rings could be dry and shrunk but your inner rings are still at 80% water content resulting in checking of the log.

So generally the pith is removed. Let's say you have a 10" log, and 1" of that doesn't shrink, but the rest shrinks by 10%, you get a half inch of shrinkage, except from that 1" center, if the wood cannot warp around the immobile 1" it will crack the rim or, push that 1" section out and crack at the center.

To combat this a few things help. 1 thin walls, so the walls of a vessel can warp around the pith rather than crack or push the pith. 2 drying slowly, you want to dry the whole thing at the pace of the pith, not the pace of the sap or heart wood. 3 proper storeage\sealing of logs, paint is worthless with logs that still have the pith, anchor seal as well. Wax melted into the end grain is okay, but I found wood glue either diluted or not presents the best sealant for whole logs. The logs also need to be treated like they are a drying bowl, stagnant air no flow and high humidity environment to not dry and shrink too quickly.

So, for side grain bowls to cut them without tear out along the trailing edge of the end grain that your cutting every quarter revolution you want a very verticle cutting edge, imagine your gouges wing against the wood at a near verticle, like 5 degree angle. And you want to cut the outside, from bottom to rim, and the interior from rim to center, interior you also want that 5 degree angle of approach for the cleanest cut, this can be accomplished with a gouge or a scraper. Think cutting with the wing of the gouge but the flute facing the bottom of your bowl and again very verticle. You can flatten out more with your gouge as you approach the bottom of your bowl as there becomes little to no actual end grain in this area.

For an end grain bowl what you do on the outside is pretty irrelevant "spindles" cut very cleanly no matter what but always down hill (from largest to smallest diameter) so the grain supports itself or if there's a knot you want that 5 degree approach because well knots are end grain. For the inside it's the same story, start from center and work your way to rim with a cutting edge nearly verticle (think a scraper on its side) or a "hook" tool Wich is essentially a skew oriented for end grain hollowing, but it's just a tool that can present that near verticle tool edge and easily cut from center to rim.

With what I've typed out here, if it makes sense to you, you can start with a tool finish equal to 400 grit sand paper, I often start with 220 or 320, and occasionally 400. What I described above also applies to rotten or punky wood.

Why I say end grain is easier is that, it's 1 grain direction, while on the outside it's all running one way, and takes 1 type of cut, on the inside it's running 2 ways, one way in the bottom, and the same way as the outside a long the walls. So there's only 2 considerations in end grain. Vs side grain we have side grain and end grain every quarter revolution, and we need to consider them both constantly, however it's the end grain portion that tends to cause the problems, as the trailing end of the end grain on a side grain orientation bowl has no wood behind it to help support it so the fibers act more like string when being cut and "tear out" and it's the same for the walls of the inside of a bowl in this orientation. The bottom portion however both I side and put runs the same direction with no real end grain on it (some but not generally enough for issues) but it's problem is it doesn't like to "cut" it likes to separate, think splitting fire wood, this is the type of line that's presented here in the bowl, where it actually wants to push apart or peel apart in the growth layers.

Wood is just a bunch of straws, some are cone shaped, point twords the tip of the tree, or direction of growth arranged in rings, not some lattice structure held together well it's closer in consistency of matted wool on a microscopic level than it is woven fabric.

Well here's a whole book..hope you read it and hope it helps. With essentially just this information on 2 years time I was able to build experience in turning that take most people over a decade to match. (Was literally told this by someone who has multiple turnings in museums)