Hi @Geoff4,
Thank you for your question about sanding cedar weatherboards and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Unfortunately, there is no quick way to sand something of this size, but a combination of power sanders will certainly help. I'd suggest checking out How To Choose A Sander for some information.
A random orbital sander is an absolute must for this job. If you could only choose one tool to speed up the process, this would be it. They are reasonably lightweight, fairly easy to control and can sand most surfaces. They will struggle in corners, but this can be made up for with other products.
A belt sander could also be handy, but they tend to be heavier and more difficult to control than a random orbital sander. They are the most aggressive type of power sander that I am aware of.
A detail sander will help with tight corners. These sanders are small in size with pointed sanding pads to allow them to get into tight spaces. They are not as capable in terms of sanding large areas but due to the number of tight corners, might be worth the investment.
Alongside these sanders, you can use a UNi-PRO Cork Sanding Block with sandpaper sheets where the power tools are struggling.
It doesn't seem like a stain was applied to the timber, rather weathering over time has given it a weathered look. Maintaining this colour would be difficult as it is essentially dirt and weathering that is giving it that look.
Protecting the timber with a clear penetrating oil is likely your best option and will keep the colour similar to what you are seeing now. This Intergrain 4L Natural Exterior Nature's Timber Oil should be a good option for you.
You might also like to check out How to finish rough sawn cedar weatherboards? where @PujDD achieved some great results.
Let me know if you have any further questions.
Jacob
