If you wish to retain an original case, you can usually find them on ebay for a relatively low cost and in reasonable condition, if you want to paint / dye yours, why not!
for the stock hardware questions, you may be better asking the question in here:
http://eab.abime.net/forumdisplay.php?f=20
and for the Gotek Question perhaps in here:
http://eab.abime.net/forumdisplay.php?f=105
If you want to see Open Source hardware projects, the links above will help. There's some very interesting open source hardware projects for the A600, from the simple, to the more difficult.
As for workbench, it is useful. If you fit a hdd, and have your games on hdd, workbench can help you get to your games, and your games can load faster than from floppy.
But, fitting a HDD and running workbench will use a little RAM for that, and some games may need extra, so a trapdoor ram expansion could help, but there are other options.
IMHO, loading games from HDD (or with an adapter, compact flash, sd card, msata, or ssd) makes life easier and better, for little cost.