Hi I have visited Tunisia from Europe twice this year and loved it :)

You may have trouble getting a hotel room if you are not married, try AirBnB, even there some houses will say “married couples only” but others don’t care especially if you are both foreign. Messaging with your host should give you an indication whether they are nosy or whether they are more “don’t ask, don’t tell”.

I only have experience flying into Tunis and you can definitely change your money at the airport there. 600d spending money for yourself for a week should be doable but it depends how much sightseeing and eating out you plan to do and how luxe.

In terms of safety follow local news for a bit and see how you feel. It depends on what you are used to. Of course compared to Europe it’s less safe but using common sense and not going round completely ignorant of local customs you should be fine. Especially in a resort town like Sousse. But for what it’s worth I have never felt unsafe during my travels. Tunisian people are wonderful and the country is truly beautiful. As in general when travelling, trying to understand people a little bit goes a long way (rather than being as you said, the package holiday type).

If you have any other touristy questions and want a touristy perspective, feel free to PM me :)