How would you stress test your own networks outside DDOS services?

Aus had a problem with the census site where everyone logged in at 5-6pm on the census date. So like millions at once.

Are there tools to stress test and build graphs about responsive times and such?

There are http benchmarking tools like wrk [0]. You don't need a ddos service for that.

[0] https://github.com/wg/wrk