I am thinking of purchasing a Lenovo W530 with:
16GB mSATA Solid State Cache Drive
It has an option for a hot-swappable drive bay
I've read that SSD is ideal for the OS and programs and that an independent drive for files and scratch drive is a good idea. Lenovo says that it will not offer an SSD in the removable drive bay. Memory seems to be a lot cheaper elsewhere and I could buy an SSD and insert it later as the main drive.
What drive (HD or SSD) and what capacity should the main internal drive be? Brand?
Is a separate scratch drive needed? Can it be set up in the removable bay? HD or SSD? Capacity?
Where should files be stored?
How should the drive or drives be configured?
Also, it comes with 2 DIMM for a total of 8GB of RAM. Any suggestions about the optimum amount and what type to purchase?
Though it was written with Adobe Premiere Pro (video-editing program, that requires more I/O, than Photoshop), this article offers some great tips, and discussions on some of the "why:" http://forums.adobe.com/thread/947698?tstart=0
It does not address the Lenovo line, but talks in generalities.
I would also post to the Adobe Hardware Forum, and give the specifics of your intended use, plus the info above, that you provided on the Lenovo. There are a ton of hardware gurus there, who can likely address each of your questions very well: http://forums.adobe.com/community/premiere/hardware_forum?view=discuss ions
In general, and only up to the current state of SSD's (they are getting better, bigger, faster and cheaper, with every generation), I would reserve their use for the OS and programs, just as you noted. For drives that see a lot of reads and writes, I still would rely on HDD's. My thoughts might well change with the next generation.
As for the media files, I store mine on my NAS, which is RAID 3. For more info on RAID, see this article: http://forums.adobe.com/message/2445490#2445490
PS - In the Adobe Hardware Forum, pay special attention to replies from Harm Millaard, Bill Gehrke, and both Eric and Scott from ADK (they build workstations, and laptops, for Premiere, Photoshop and After Effects, and know their hardware.