Depends on your check book brother. With the 4- 500 watt halos you will need a 1200 continous watt or larger genny. If you add one more you will need a 2000 continous watt genny.
You could get by with a smaller genny but it will work it harder.
Honda EU gennys are bad to the bone and the yamahas are awsome also. I have used a WEN 3500 for the last 3 or 4 years and got along just fine and its a $300 genny. I have two honda eu 2000s on the way and they are bout a grand each.