Here are my two bits on covers. (My apologies in advance for the rant.)
If you are planning a multi-book series - pick a solid name for your series. Put effort into logos and iconography that fit the motif you are trying for. It's a lot easier to look cohesive if the text is the same. *It's also easier for you if you don't have to start from scratch every time you put your title on the cover.
When you get ready to sell your work, pay attention to the cover art trends in your genre. Your cover should be eye-catching and work for your brand. If you are aware of the trends, you and/or your cover artist can make educated designs about what you want your book to look like. For example, the big trends right now in novels are close up chest shots of the hero/model, a single magical esque object, and lots of swirling light and bold colors.
The covers are eye-catching and sell well, however, a newer writer might not be lucky enough to make a profit in that wave.
But ultimately, your covers should fit the vision in your head and make you happy. I went through several versions for my book covers before I found something that I liked. They don't "match" per say but I like to think people would recognize them as a series. They're selling so that makes all the difference.