Battening a Garage

Hi,

I am renovating/extending a Queenslander in Brisbane. The house has been raised on steel posts, and I am building under the front area of the house for a garage (rear area is built-in living area).

I will be using 3m timber battens vertically mounted to still retain the Queenslander look/feel. These will be nailed to 3 horizontal rails running between the steel posts (the rails are not mounted on the inside or outside surface of the posts). Rail span is no more than 2400.

My questions:

1. What is the best way to mount the rails onto the steel posts? I have considered:

a) welding brackets to the posts to bolt the rails to (would need a lot of brackets) or

b) fabricating a frame comprising of the rails with vertical studs at each end and then bolt the frames between the posts (this may look too bulky on the inside).

2. What is generally used for the battens. I have been told that treated pine palings 100x16 are generally used, but are these of sufficient quality/thickness for the job? I hav considered decking, but this would be very expensive ($300 for palings vs $1500 for decking).

3. What would be the preferred gap between the battens/palings?

I know these are somewhat abitrary selections, but would be keen to understand how it is generally done.

Thanks,
Philip.