You could use the Alesis FST/Connect external hardware to interface between an HD24 caddy and your FireWire port. With that in place, you can run the Alesis software or the 3rd party HD24 Tools software for transferring recorded tracks to your computer. Note that an HD24 drive is not visible directly to a Windows or Mac operating system and that you have to use the special software for the track transfer.
An alternative is to get a Vipower caddy receptacle and mount that in a 5.25" front panel slot in your computer. You would connect the rear of the receptacle within your computer chassis to power and an IDE (parallel ISA) port. This makes it easy to hot-swap caddies between the HD24 and your computer. You can run the HD24 Tools track transfer software with this arrangement but not the Alesis software.
I recommend you visit the Yahoo HD24 group for further information.
Avoid the Ethernet connection to the HD24 for track transfer if you wish to preserve your sanity.
As far as DAW software is concerned, I would give serious consideration to spending a very few $ on Reaper. It will probably do all you need, but if you did wish to move on to something more expensive, you will have had an excellent learning experience for not much money.