Help - Stain recommendation for pressure treated new pine pergola in Florida

Hi - Thank you so much for this very helpful forum.  I really appreciate any guidance.  I am reading about differences for vertical surface verses decking and and wanted to get advice for my specific situation which is newly built pergola of pressure treated pine installed 2 weeks ago. My contractor is stating that I do not need to wait to stain if not using a light color stain.  I am looking for a fairly dark brown that is not red and from everything that I've read am preferring to use a water based product.  The pressure treated wood is not pretty so I would like to be able to still see that it's wood but am not wanting to accentuate the grain and preferring it look more consistant in color so that you can see it's wood but hopefully not bring out every knot and inperfection.  I want to make sure that the stain looks even and not streaky.  I am not sure what products to use - the contractor typically uses Behr and have read that not being good as well as don't love thier color options.  I am thinking I want either semi transparent or semi -solid finish.  So multiple questions here 

- do I need to wait to stain this wood?

- does it need additional prep prior to staining?

- which stain products are easiest application and will give me the finish and color options desired?

- any views on semi transparent verses semi - solid and what's the difference?

Thank you so much for any thoughts!!