Close. A CD has (roughly) 750MB data for 80 minutes of music. So that's about 60 seconds for 10 MB (10240kB) or about 170 kB/sec. A bit more for the (serial) overhead. Try it.
Where do you live? There are literally dozens. Lowest price I saw currently in UK at under $300 if the guy still has them, here
Yes, you are confused.
The only software decoder from Sony is hidden deep inside SonicStage versions designed for the RH1. It requires the unit firmware to output MD data direct onto USB, which (we think but are not 100% sure) none of the other units is capable of doing. There exists an open source project that can do this, but ONLY with the RH1 as starting point to generate the data streams. Right now, almost no one has generated and stored any files in this format, which is not of itself a barrier.
And which Sony has used first hardware, and later major encryption, to prevent.
What's that?
You will, I think, find that that is not possible. The only digital OUTput comes straight from the master chip (after decoding from ATRAC to normal S/PDIF. There's an ATRAC ENcoder that is separate in a number of units (not the most recent portables, IIRC), but the decoder is built into the ATRAC chips. You can take a look at any of the schematics. Even the MDS-W1 uses the same chips. The only difference there (and on the combo CD-MD decks) is that the hardware decodes and encodes in real time, so the transfer is "effectively" digital. In reality it's not. Show me where the digital signal is available, and I will believe.
That's the method I have used for almost 10 years, and it works. Go ahead and waste your time.
In terms of marathons, you might be able to coerce two of the "pro" units into relay-playback so you could automate things a bit. But for that money you can afford an RH1.