All resistors are approximations to the ideal resistive behaviour the device manufacturers and users want. But we can only get close. Sometimes we are so close that the deviation from ideal behaviour is of no concern in the respective application, sometimes it hurts.
The most important thing is to know that each resistor has a datasheet. A serious developer will always consider this datasheet, know his requirements for the application, and find out if a particular device is a good choice by comparing both. It sounds too simple, but many problems have the root cause that this is not properly done.
If you want to master electronics, you must, among other things, look at a lot of datasheets, learn about the way device properties are explained there, and what the data means. While many understand that doing so is important for active devices, passives are often neglected and treated as if they only have their primary value, resistance for a resistor.
For instance, each resistor comes with a so-called 'parasitic' inductance, simply because current flows through it, and current causes a magnetic field, which stores energy and makes the behaviour time- and frequency-dependent. Since Ohm's law tells nothing about time or frequency, this is an important issue that cannot be avoided. It means non-resistive behaviour in the sense that it is not according to Ohm's law.
7. It is not actually necessary to know the material. The datasheets may or may not tell what it is. But it must tell the behaviour, which depends on the material used.
8. Even the smallest components can be soldered by humans, but you need a microscope to properly see what you're doing.