"Might look like this." No it will not! Please do not expect your yard to be 'weed free' because you're using mulch. When my mulch was added, using fabric landscape fabric(useless!), the weeds kept coming, and coming........you get the picture! I've removed the fabric 'weed barrier', and am in the process of having black plastic installed, even though i've been advised against it by a few forum members. Like yourself I was envisioning a park-like, floral 'fiesta for the eyes', but have gotten a 'nightmare on Elm St.' instead. I had what I thought was a professional landscaper, and would have thought i would have been advised re:advantages/disadvantages of using mulch. What it's really about is what's going in their pocket.

In terms of your question about curved paths - I can see why you might decide on a straight path given the size of your yard, but if you have a straight path, I think it would be better to have curvature in your plantings - right now everything is in straight lines. Most (but not necessarily all) landscaping pictures that I see have some curves. Or in the case where the design uses only straight lines, they will have for example, one rectangle, and then another that is jutted out from the first, and so on in such a way that the various rectangles actually visually look a bit curved. This is a picture that might show a bit of what I mean. https://www.houzz.com/photos/paver-walkway-traditional-landscape-columbus-phvw-vp~237790 In terms of your question about what type of walkway to use - my preference would be a solid surface as per your second picture. I think that the first picture looks a bit more like a casual path that would be in the back yard, and not in the front yard.

Also be so so careful of anything non native that promises to fill the in the area super fast with no work at all like Vica vine, ivy, snow on the mountain, etc. They are invasive and will be way more work in the long run, please please don't do it. In my experience so far, anytime you add a whole new series of plants or shrubs, it is a process and a lot of work. That is also why a photo or an idea of what is already planted there would help. Perhaps there is a base already to work with that could just be tweaked a bit. That being said I have seen some long term fill in success with day lilies or ferns. Sometimes hostas. They do take work to get established to that level though. Of course, I also have no idea if its appropriate for the climate, light and space you have going.

Irises and certain other perennials aren’t difficult to grow, but without regular deadheading can look messy. Since this is a rental, plants that need regular hands on maintenance aren’t practical if you want a tidy appearance. Around me (acid soil and cold winters) panicled hydrangeas are long blooming and if one is chosen to fit the size of the bed, never need pruning, just a once annual deadheading if wanted. Rhododendrons such as the PJM series are hardy, evergreen, unfussy in acid soil, and have cheerful spring flowers. There are lots of choices that will provide a nice looking bed, but without giving us a location, you will need to research options for size, hardiness and maintenance needs.