Where im confused is why you think PHP isn't commonly used. It powers the grand majority of the internet, and as a language designed entirely around making websites (as opposed to general purpose languages like Java that have crammed in an http server to make it work for websites too), its a language that's incredibly easy to jump into, and offers a lot of flexibility and versatility on how to navigate web facing challenges.
Also don't kid yourself about the node "one language" ecosystem. You will find yourself often visually confused as you jump between editor tabs which .js is aimed at the browser, and which .js is aimed at the server, and gets even weirder when using js based templating engines. (This is why in my node projects with a front-end, I use Angular, which uses TypeScript),). JS was never intended to run outside of a browser based VM context, its just yet another language we've jimmyrigged an http compatible socket listener into and given filesystem access.
If you're worried about wasting your time jumping into bed with PHP, don't be. Its not only extremely widely used, but after 20 years its still incredibly relevant, high performing (you will be shocked to see how fast php7 actually is), high paying (yes, six figures), and the language itself has evolved leaps and bounds into a multi-paradigm beast of a toolkit bespoke to solving web challenges.
If you liked Spring, check out Symfony sometime. Its a PHP7 web framework that takes a LOT of inspiration from Spring, and pairs up with Doctrine, a PHP7 ORM that takes a great deal of inspiration from Hibernate. The company that makes Symfony, is also the same people behind Twig, which is so ridiculously good and popular, its been ported to pretty much every language including Java and node.
As for free packaged out of the box storefronts, Magento is a total beast of a package, and isn't for the feint of heart. But it is also THE most complete and ridiculously configurable self hostable e-commerce system you'll ever come across. Many web professionals have made entire careers completely around Magento. I am not one of them, but I have used Magento, PrestaShop, and several others, and I keep coming back to Magento. Outside of hosted shops like Shopify, Magento is, as far as I'm concerned, where you wanna be for a totally custom, plug-in based shop front for a website. The only time I'd recommend different, is if a customers website is powered by WordPress, then WooCommerce is where you wanna be.
