the japanese samurai irons, as sold by axminster, are generally thicker than modern Stanley & Record irons, but not as thick as, say, a Hock. They're laminated irons, in much the same was as Jap chisels are. They're considered very good - well worth investing in - being laminated, the actual cutting part is hardened to a very high rockwell rating, possibly even as high as an A2. They hold their edge well, but are brittle - shouldn't be a problem in a plane.
One potentially useful trick is to have a samurai and a hock - that way, with different iron thicknesses, you get different plane mouth openings with the same frog setting (from DC, volume 1)
The cap iron - well, I personally actually sharpen my cap irons! I want the interface between the plane iron and the cap iron to be as close to perfect as possible - no gaps for shavings to get caught in, so no choking. What you want to aim for is the ability to sandwich a rizla paper between the cap iron and plane iron, and not be able to pull it out. You want the cap iron so it comes to a point, which is the contact with the plane iron - you definitely don't want the heel of the end of the cap iron being the contact with the blade, cos you've got an instant gap there, and so a choke point.
Also, you want the leading surface of the chip-breaker part of the cap iron to be smooth - sand it, and even wax it - helps shavings go over and curl nicely.
Yes, you can fettle a modern cap iron very nicely - no need to invest in after market ones; the Clifton stay-set 2 piece is a nice bit of kit, but a luxury. Lie-Nielsens new cap-irons are thicker than the old, I understand, and help reduce chatter - not experienced one though
