EZGO RXV - Give me the good and bad

I am considering a used EZGO RXV. I have read a lot of good things about them, but I also would like to know what to watch out for.
Are there certain years models that have more issues than others?
What are my upgrade options for speed/torque?

My usage would be 2 adults and 2 kids on pavement with moderate hills. I would like top speed around 23 MPH. Will a stock one do this? Or do I need some aftermarket upgrades.

Thanks!