I would look for an iPad 2 (the one without retina) instead of a 1. If your market is anything like ours, there isn’t THAT big a difference in price between used 1’s and 2’s.
The iPad 2 has a dual core A5 processor whereas the iPad 1 has a single core A4 processor. This is a pretty big step up and with iPads being available new for around 400 euro, the difference in price between a used 1 and 2 can’t be more than a few 10s of euros and I would most definitely go for the 2.
The 2 will do anything you need it to I think. After all, iPad apps are just that, apps designed specifically for the possibilities and limitations of the platform.
Greetinx,
C.