It is 1 5/8 inch .
Yes it is available in 16 ft lengths
No the longest it is available is 16 ft length
Wolmanized is a very old brand name for pressure treated wood. If you want lumber that is kiln dried AFTER treatment, head to your local store and see the pro desk. They can likely special order material that kiln dried after treatment.
I believe they will cut it to any size, or you can purchase that same board in a smaller length...
I would leave gaps to let rain run off. Put a nail or screw between the boards or you can eyeball it. I usually leave a 1/8" gap. I've not had a problem with shrinkage.
Premium pressure treading decking has a better visual appearance than standard pressure treated decking as there are fewer knots and less wane (bark edges)
Please speak with your local PRO associate to discuss special order options.
You should wait at least 90 days before staining . That gives the lumber time to dry out.