Thanks for your reply.
Bear with me, because I’m coming to WordPress from the Joomla world, and the operating methods are different.
So, let’s say I have ‘travelgear.com’ as my main domain name, and I have three clients: planegear.com, traingear.com, and automobilegear.com each of which has a different merchandise assortment. When a customer goes to ‘travelgear.com’ the URL directs them to my WP company site. But when they go to ‘planegear.com’ the site’s store would show only air-travel related products, pictures of aircraft, articles about traveling by aircraft, ads from various airlines and so on. Same idea for trains and cars.
Yes, separate DB tables are fine, and after finding and skimming through ‘The Ultimate Guide to WP Multisite’ I understand more clearly. It seems that changing themes and content based on URL is more easily managed by a plugin than natively in WP itself. If you can recommend one, that would be a huge help.
Thanks in advance!