You seem to have kept that quiet Prawn. YH isn't my area but there is lots of advice on Tunisia in general on this forum. Just relax, remember if you don't want to barter there are plenty of fixed-price shops around, but bartering is their national sport, and can be fun. La = no; ghali barcha = too expensive; m'andee floos = I have no money. Always start by offering about a third of what they want and work from there. Transport is cheap but in a taxi either 'negotiate' a price first or insist the driver puts the meter on.
If you need to phone home do not use your mobile or the phones in the hotel but the public 'taxiphones' which are widespread throughout Tunisia.
I'm sure you'll have a great time. Look through the rest of the Tunisia forum and don't hesitate to ask if you need any further help.