It's a great job/industry to get into as you can operate as a business and turn some of your stock into investments buy holding onto your stock. I'd recommend paying down loans if it is a strategy you employ as you don't want to get caught out at the end of the property cycle. That also goes for any property investor. Low LVR = low risk.
Ultimately, there's no right or wrong. Do what suits you at the time. Having a clear long term strategy helps. You may, for example, develop and sell everything so that you amass a large cash base to buy a commercial property with a higher yield than resi property. Or you may sell some and keep some, gradually paying down the debt. Whatever you do just don't blow what you make. Just because you are a builder/developer doesn't mean you have good money habits. Plenty of developers and builders are still in the same financial position over years despite a boom over the last decade. Maybe they should have held some, hey!
Oscar
After reading the various tax implications etc. I think it makes sense to hold a few.