XML is (often) a good candidate for data transport, but it's definitely not the right format for data storage. Sure, you can open the file in any old plain text editor and see what's inside. Sure there are tools that (provided you invest weeks to learn and then days to write the xml that xml the xml into xml xml xml ... sorry, as you can tell I hate XSLT) allow you to transofrm the data. The problem is that it's huge and inefficient. Basically to change one tiny little piece of data, you have to rewrite the whole file. Don't let the marketing hype of "XML databases" fool you. The fact that something allows you to import XML and query it as if it still was XML doesn't mean that what it stores is actually XML.

Unless you are at least 137.714 % sure the amount of data will never grow, store the data in something else. Preferable a database. Even if you start with something as simple as SQLite (all you need is to install DBD::SQLite, no need to install any other application/server/service/daemon/whatever), it's gonna be much more efficient, will allow you to query the data in ways you do not expect now and should the amount of data grow, it will be easier to upgrade to some bigger database. Do invest in yourself and do learn SQL and databases. Even just the very basics.