For a truncated girder in a hip end, span by station divided by 4 will give you pretty much the total area supported. However, note that there will be a small area of roof beyond the girder truss where the top chord of the jack truss and adjacent trusses are extended and bear down onto the girder truss. Figure 2 in Gang-Nail Guide Line no. 4 will help to explain this. The Guide Line can be downloaded via this link https://www.mitek.com.au/wp-content/uploads/2021/05/GN-Guideline-4.pdf.

We don't generally get involved in individual design projects, but we have a Technical Design Manual that will answer some of your questions. It's titled Domestic Timber Deck Design and can be downloaded free of charge from our website via this link https://www.woodsolutions.com.au/publications.

We understand that sawn timber which is clean and untreated (ie. not preservative treated) is readily recyclable into mulch, animal bedding, particleboard or fuel. However, you have to enquire with local facilities if they will also accept plywood for recycling into any of those applications. It varies between facilities. Most plywood made in Australia is made with either phenol-based resins (A-bond) or melamine urea-formaldehyde (B-bond) that are very stable and strong.

From your description and the image attached to your message the most obvious type of timber would be the group of Peltogyne species commonly known as "purpleheart". You will find more information about purpleheart on the Fine Woodworking website via this link https://www.finewoodworking.com/forum/where-is-the-purple-in-my-purple-heart. It is a South American species not widely stocked in Australia but available from specialist timber suppliers.