The op original question is "how to begin a career in developing"
There is no harm in trying something new but if the op makes 140 k per year and sold a business he started few years ago for 580k how is he going to beat that being an inexperienced property developer?
My very first development made me more than that and all I had was $100k for deposit, stamp duty and subdivision costs. It really isn't that difficult if it's something suited to you so Gary could beat that theoretically.
Also the only way to not be inexperienced is to get said experience, what's the worst that could happen? A bit of money lost, not the end of the world.