The Arduino microcontrollers are mostly based on the AVR family of microprocessors, although some newer types use Arm. Programming is done using the very good Arduino GUI. The language used is C or C++ based. Many libraries exist for Arduino, making software development less of a chore as very often all the hard work has been done by some-one else and all you need to do is glue together the parts.
Swonk sources his Arduinos from Banggood.com. They have a good range of microcontrollers and related bits and pieces. Prices are good and they include shipping.
The cheap Chinese Arduino knockoffs sometimes use non-standard USB serial adapters. This can be a problem on Windows or OSX because you need the matching drivers. When I've had problems with these, I go to my Linux system. The Linux USB serial drivers don't care that you're using a knockoff chip and just work.