Hmm it probably helps to put perspective on what you are doing, right now you have set up a mix of traits defined as x crossed with y which is termed a chimera. These generally don't look right because the focus is on the parts in general often in a literal context. To move beyond that and blend them into a greater whole it probably pays to treat the description as someone trying to describe an alien creature and then parse what they are really observing instead. For example Europeans described the platypus as a dusk mammal hybrid because those were their closest points of reference but they aren't actually such a chimeric cross.

First and foremost at least you will want to account for proportionalities and scaling since you are mixing disparate parts from very different organisms.

But if you really want to get into the how's and whys of making things fit together it also helps to keep in perspective that traits such as eyes ears skull morphology and such have functional purposes. For example if the aspects of a cheetah you are looking for are the cheetah like build then it helps to know that a cat like build IRL seems to have arisen independently multiple times over evolutionary history among quadrupedal tetrapod ambush hunters, from the gorgonopsids of the Permian to the crocodylomorphs of the Triassic. Cheetahs among cats focus particularly on bursts of speed with the coat serving to break up the animals silhouette in the savannah and make it easier to ambush prey, So you might want to incorporate those aspects of an ambush hunter into your elves. For example perhaps they are lithe facultative bipeds at home as much on 4 legs as two with dexterous clawed hands adept for climbing.

Do you more specifically want the ears of a cat? Those have their form in order to give the animal more precise directional hearing by limiting what they can hear effectively to specific directions they can shift the direction of their ears to pinpoint the location of prey. So you could adapt a hominid type build animal to utilize that kind of directional hearing which also fits in line with the long pointed ears of elves though do take note that the positioning of the ears on the head should if realistic biomechanics is the goal be oriented based on the animals typical stance when hunting . I.e. cats ears are high on their heads because they generally crouch down low to the ground creeping up slowly on prey until they are in range to pounce.
The reason most beast men feel like low quality chimeric crosses is because they don't take account of the whys of traits such as how directional focusing and orientation is going to come at the cost of the ability to readily discern what another person is saying from a direction other than where their ear is oriented meaning ear posture will be highly important to them as much as we care about if another person is facing us when talking to them. The placement high on the head also means they are likely low to the ground much of the time and thus will probably only be facultative bipeds or very short else their ears placement would come at a cost of hearing things from below their head placement without providing much benefit in return.

Now it will take more creativity to incorporate the cross kingdom plant aspects as again you will need to parse what specific plant characteristics you want them to have. Do they look like plants say having bark like skin and grass blade or pine needle like fur? Or are they plants with the addition of muscles and a cardiovascular system allowing them to move and act like animals who say hunt prey to acquire the nutrients they need for photosynthesis. Or are they say animals with symbiotic algae growing on them or incorporated into their tissues?

You will need to come up with and answer these kinds of questions for each of your ideas if you want them to fit together naturally. There are no easy answers I can't read your mind and this is a DIY community anyways.