I ended up using the cork, but mostly because that's what I had prior experience with. I don't think there's any significant difference between the 2 types functionally.
For curves: Most locomotives will be fine on 11ish" radius curves, but the general rule of thumb applies: Wider curves = better. I say 11ish radius because some manufacturers are 11.25 and others are 11.5, etc. I have several 11.5" curves on my layout, and all my locomotives can navigate them without derailing, but the longer ones look silly, almost "cartoon-like," with the front and rear parts of the loco jutting out over the curve as it makes the turn (which can cause derailments as the car being pulled behind it tries to follow the rear end out away from the curve.). But... all these tight curves are on the part of my layout that would be a "short Line" railroad, serving local industry. So I use shorter loco on those lines anyway. I also tend to only use sharp curves like that when making a turn out of view, or at least partially obscured, like going into a tunnel, or around a bluff/ridge. For Mainline, I tried to keep everything 13" or larger. 13" seems to be where I don't notice the cartoon-like tight curves.
For inclines (grades). Rule of thumb is "keep everything level." grades add a ton of visually appealing attributes to a layout, but, even the slightest grade will affect your locos ability to pull long trains. On a rally flat surface, with rolling stock that is in good condition, my Kato SD70Ace can pull roughly 30 cars without issue. But... the mainline has a 2% grade that is only 2 feet long, and the loco starts spinning its wheels (losing traction) at around 25 cars. Woodland Scenic sells incline sets at 2%, 3% and 4% grades. Most locomotives, pulling a handful of cars, will be fine going up 4% grade, but much more than that, and it may not work well on that steep of an incline.
Inclines:
2% grade will rise 1/2" every 2 feet. Technically, it's 2.0833%. A perfect 2% grade would be 1/2" over 25" but the WS kits round to 2-foot sections.
3% grade will rise 3/4" every 2 feet
4% grade will rise 1" every 2 feet.
Grades are neat, but to be honest, I ended up with 2 completely different tracks: One down at sea level, and one up in the hills. I have a pretty big layout, and I was having a hard time finding a stretch 8 feet long with few curves and no turnouts. I wanted to keep to a 2% grade or less, and it takes at least 8 feet to rise 2 inches. (HINT: try to keep all turnouts on a level surface. Using a turnout on a grade is not best practice). Which brings me to the incline itself... The incline needs to be a flat surface too, just on a grade. That's what makes the WS risers and incline sets so nice. They are really nice, but you could always use plywood and/or foam boards to build the "ramps." I had one area along the "mainline" where I wanted the train to go through a high spot, so I used one of their 2% "Incline starter sets" which has several 2-foot long inclines that go from ground level to 1/2 height.
Here's a visual. You can see on the right side where I used the incline starters to raise the track 1/2" as it loops around the bottom right. You can also see how I simply left a void in the 2" foam boards for tunnels.
Super simple to create a tunnel access hatch... I used "dead" trees super glued to the foam surface to act as handles. The access hatch comes in handy for track cleaning and clearing derailments. The tunnel access hatch is a few inches wider than the tunnel underneath, so the access hatch doesn't get pushed down into the tunnel from above.
Hope this helps. I'm sure you feel like you're drinking from a fire hose, but it's all good! Lots of things to lean, and plenty of good people here to offer up advice!