Hi and welcome
It sounds like the previous owners may not have taken great care of the little 500 unfortunately and it's fallen to you to try and keep it going.
Here's a link to a washer nozzle, should just be a push fit so easy to DIY.
Regarding servicing, it either needs doing at a particular mileage or yearly, whichever comes first. What type of service it needs is dependent on the age/mileage. The handbook should contain a service schedule so you can get a rough idea of what needs doing. The likelihood is that it's just an oil/filter change and visual inspection of brakes, etc.
If you're not looking to start getting into your own maintenance, let us know where in the world you are and maybe someone local can suggest a trustworthy garage