I hadn't bothered giving links, because I had assumed the OP was capable
(You really should get yourself a newsreader and a newsserver instead of that crap Google Groups interface that always messes up quotations.)
Avoid Microchip's microcontrollers if you can. They come in big packages, which can be nice if you are making a board in your cellar, but the PIC cpu is hideous (it competes with the 8051 for the worst cpu ever to become popular). Their non-microcontroller parts are usually good.
The ADS8344 will do a fine job, run with the internal clock (to save you having an external one). Forget the "busy" signal, it would just complicate matters. Don't daisy-chain them - they cannot easily daisy-chain. Instead, connect the devices mostly in parallel but with separate chip selects to individual IO's on the FTDI device.
Mostly Linux, some Windows (I have an old XP machine, but the end result usually has to run on XP and Win7). I do most of the development on Linux, however.
You can choose yourself how to configure the chip. By default, it registers as 4 virtual comms ports, but you can access it with the library code from FTDI and override the modes. The application notes from FTDI about using the chip for SPI are definitely worth reading, even if you use pyftdi instead of FTDI's own libraries.