Port El Kantaoui is lovely, which Hotel are you staing at!?
Everything appears 5 star but dont let the journey from the airport to the resort put you off. Every building looks unfinished, and they are, for a reason, unfinished houses in Tunisia avoid 'council tax' if you like, so the owners leave the metal rods sticking out of their roofs!
July will be HOT, take plenty of cotton clothes and sun cream. Is your mrs Blonde? my other half was and you 'can' experience gawping, staring, etc. However, El Kantaoui is resorty enough to not be too bad. Its when you go on the excusrions (like to the Medinas, etc) that you'll get people hassling. Its not unpleasant, but it can be intimidating, you and your Mrs just need to be firm. They may try to grab her arm to show her something she might need to buy, you just need to be polite and say your ok thankyou.
Also, if you speak French, it goes a long way as this is their primary (alternative) language, they speak this as much as Arabic.
The hotels are fantastic, and as I said, give you a real 5 star sense. So enjoy it...
Excursions to look out for - Do the desert thing, (not the one where you stay overnight, as its pointless paying for a hotel room otherwise, and some people can be badly ill).
Roman ruins is good, and a visit to the medina. Also, do the casino if you can, thats a really good experience.
Make sure your up to speed on jabs, etc (Malaria, and stuff)
Hope this helps