> I'm a bit at a loss on how to install it !

If there is a release for your os/arch, then download the binary and put it in /usr/local/bin/jcb (you may need to chmod +x it). Otherwise you'll need to get golang and run "make build" which will get you a ./jcb binary.

> Is it intuitive to create transaction in advance to simulate a budget ?

You raise some interesting points that I need to think more about. I've just been making placeholder transactions to pad out the budget while I don't know exactly what the months transactions will be. It makes it hard to know where you stand midway through the month. At the end of the month you can see exactly how much you spent, but you can't see how much you budgeted once you delete the placeholder.