[The Fifth Horseman]

Personally, I'd advise an 8-meg GPU, maybe ATI Rage XL, if you want to play certain Windows games. For pure DOS, 1 MB will do ideally, as it will do for basic Windows operation.

2x1,5 GB HDD doesn't sound like a good idea, size-wise I'd suggest something more like a decent 4 GB, and second 1-2 GB one.

CD-Rom drive isn't that important. You can fit in a modern 52x drive without any problem and it will work perfectly. Actually, it's even better - that speed will provide much better data transfer rate. One thing you might consider is to buy a drive that has a built-in audio player with play button (separate from eject), volume regulator and an audio socket on its front panel (that's how they used to be back in the days).

You can buy a floppy drive at any computer hardware store. Any one will do, they practically haven't changed in last decade.

You might try DOS 7.1, it has complete support for LFN and FAT-32.

If you get two hard drives, have one of them run Windows (95 OSR2.5 is a good idea, since it has USB and FAT-32 support, 98SE will lag too much) and the other DOS.

Also, if you are so certain you'll get two, you might also consider getting the following things:
2x IDE hard drive rack (~15-20 $ each, depending on the model)
1x USB 5,25" IDE drive enclosure (~40-50 $)
One of the racks goes into the oldschool box and holds one of the HDD's, the other rack goes into the 5,25" USB enclosure. This way, you can use the enclosure to transfer data between two machines at an insanely high bandwidth, without messing with LAN or burning stuff to CD's.
Actually, if you get a Midi-sized case (with 3x 5,25" drive bays), you can consider getting a third rack - by attaching the racks to separate IDE channels and setting each drive as a Master on the given channel, you will be able to run two systems without messing with Dual Boot and freely exchange data between both drives.