Mate,
Make sure that you read the manual. Start in factory presets and adjust from there.
People on here will give you settings but they are basically useless unless they are actually onsite with you as the ground can change dramatically over a short distance
Ive seen newbies turn up at Hill End with their shiny new 4500/5000's and cant get them to run quite enough to detect. When asked about their settings from they mostly tell me they got them off some bloke on the internet. One bloke even turned up with settings from a guy in USA and wondered why his machine was screaming.
With regards to the DD coil. Dont let people on here put you off using it. I have recovered over 3 oz of gold from the gullies around Hill End with the 11 DD coil. I work the rubbishy areas only digging the good signals and leave the rest to the mono brigade.
When I first started using the DD coil I dug over 300 rubbish targets just to prove that they were crap and all were.
Do your own testing and come to your own conclusions
Just get out there and enjoy yourself,
Bob