I would do metal posts and railings either glass and metal or metal spindles too. Are the pictures of your deck? The rot I see in the one picture looks like the boards were installed on a solid piece like underlayment for a inside floor. You need air to keep rot at bay . I also use an extra layer of wood treatment on anything that touches the ground.I have to say there is nothing attractive about seeing the under structure on a deck and the critters will go there no matter what you do, friends of ours took chicken wire rolled it up under the deck to make it impossible for the critter to live and then covered the exposed area with lattice it has worked for years.

As a I mentioned, I will not be using metal for my railings. They will be a pressure treated wood frame and glass panels like the current design. Lots of reasons for this decision.

Yes, the current deck was designed poorly and there are boards sitting on top of other boards.
In that picture, a 2*8 is sitting on about 4-5 joists that have been nailed together to provide a platform for it to sit on. The new deck will be framed properly to avoid those wood-on-wood issues.

As for "there is nothing attractive about seeing the under structure on a deck" we're just going to have to disagree. I think lattice looks disgusting and a well framed structure with 6" posts, ornamental post base and post to beam hardware and large beams is quite attractive. :)

Be sure to check the manufacturers installation instructions on composite decking. Certain brands allow 16" O.C. framing others want 12" O.C. Whether you do composite or a PT deck its a good idea to run a good building tape like Vycor or ZIP Tape over the top of any double or triple beams. That keeps the water from getting in between these pieces of framing. I suspect that is what happened in the first picture.

Thanks. I like the feel of a sturdy deck so if I go with any composite, I will probably shrink the spacing from 16" to 12" no matter what the manufacturer says. Agree re the joist tape. That is in the budget for all beams and joists (even the single ones.) The joist tape would have helped with the first picture but there is a better way to set up the framing in that section so that the one board that divides the two sections is resting on joists that are perpendicular to the board instead of trying to build up a joist to be 8" thick so that the board can rest on top.

We have mixed Ipe wood decking with P.T. framing and posts; it all turns a similar grey.

So by choosing a grey colored composite, all components will match.

If you will be staining the whole thing brown, I can’t help - that is way too much maintenance for me!

Also, a cantilevered design helps hide the framing underneath. Don’t know if that is possible with your deck layout.