** I believe the floor is 1/2 inch plywood. Is this strong enough to support it, or do I need to shore it up from underneath? **
I believe that should be sufficient to support the weight of the product but you should consult the appliance installation instruction to be sure and also to see if any clearance, etc. is required. If you can't get those instructions in advance from the selling dealer, they are often available for download from the appliance manufacturer's web site.
BTW. I suggest you don't make any final preparations until you actually have the product in hand. Manufacturers do state on their dimensions, etc. "Specifications subject to chance without notice". It doesn't happen often but can, leaving the consumer to redo the installation.
You can read some other appliance installation tips at the following link: