Thats sounds sufficient enough. Just remember to keep the length of the ground wire as short and direct as possible to the ground rod. Electricity likes the path of least resistance so if your coax length to the radar box is shorter you may not be discharging the static build-up as well as you should.
As far as lightning arrestors go, they are a good idea. The ones that are designed for the frequencies that radar box operates on may be a little costly.
The standard ones that work from 1Mhz to 2Ghz may have high losses on the higher frequencies. Polyphaser makes commercial grade lightning arrestors specifically for high frequencies with low loss.
http://www.polyphaser.com/products/DSXLhttp://www.polyphaser.com/products/prod/coax/sx/The polyphaser DSXL covers the high frequency of radar box but is a dc blocked lightning arrestor so if you decide to use a pre-amp at the antenna and power it with a bias-tee (power over coax) this one wont work. You will need a dc pass lightning arrestor, polyphaser makes those too.
Just to go a little off topic, what antenna and coax are you going to use?
The reason I ask is because from my experience using radar box you will have high signal loss with increased coax length. The type of antenna (Base style with high gain) may help compensate but overall you may experience higer losses.
You may want to test that set-up before you finalize it to make sure that you have increased the number of aircraft as well as the range they are received at.
Just something to look for and keep in mind.