Thanks guys for all of the very detailed/concise answers. They are very helpful.
I hadn't thought about the grain running different directions in ply. Only thought about the glue laminations and dimensional stability as positives.
I am definitely going with L girder construction so if there are any additional tips regarding drilling/screwing into the edges of ply they'd be appreciated. It's good to know that using ply can be cheaper than dimensional lumber too. That seemed to vary based on where I shopped around.
I used pine 1x4s on my flooding cellar layout benchwork 18yrs. ago and it seemed to hold up fine (amazingly) and it's always damp down there and gets to freezing in the winter, so I'm not " too" paranoid about using pine upstairs but wanted to hear from both sides while I'm still in the track planning stages for some time to come.
I wondered about buying from outdoor lumber racks as opposed to Home Depot, etc. I'm asking now, because I'm thinking about starting that stockpile in the layout room now before the track planning
gets done. It should be in there for more than a couple weeks maybe a month before any cutting takes place. I do like the ease of working with the pine but if I moved to a warmer climate someday the ply might adapt (or not adapt) easier. All things to think about.
I'll want to construct my benchwork (around the walls-likely a folded dog bone) so that it can be moved
should I ever move so weight is a consideration to some degree. (I want to use a ply top and roadbed base rather than foam.)
Thank you for taking the time to help me out. I appreciate your taking the time.