Hard to comment on the front yard with that very limited photo. How about showing some context and the full front view?

More pics (Apologies. the construction makes it a little tricky to see)

for the amount of work and money you're putting in, hire a landscape designer. Are you in California? Go on APLD.org and do a search, it'll help you get the most bang for your buck. As a profession, we're pretty awesome.

I have a 5' wide side "yard". It originally had bark dust over landscape fabric, then I pulled that up and grew sedum groundcover along the side in the front one quarter of the path. Behind the gate is a utility area so it was just packed dirt there. Last month we laid landscape fabric and added about 3" of 1/4 minus crushed gravel. It was easy to rake smooth and I like the look. So I don't think that's too much gravel, and you could even forego plants in the side yard and use very wide pavers. I'm not sure what will grow well between two houses. You can top the crushed gravel with an inch or two of decorative washed gravel, which comes in a few sizes.

The back looks a little barren to me.

I find it curious that you poured concrete before having a fully developed plan.

The fenced in area is quite small. I'd limit the variety of plants and keep it simple. I don't see room for a tree there.

Do you have a plan for watering?

This looks a lot like some of the older San Diego neighborhoods near me. Some of them have gardens with the modern look you are going for, and it works very well. I would agree wholeheartedly with mayflowers above that succulents will have the sculptural look to go with your house and garden plans. For height you might be able to squeeze in one carefully selected palm, one that will remain in scale and not cause problems with your overhead wires. More easily contained size-wise would be a large slow-growing succulent, such as Aloe ferox. If you are in California, it will be worth the effort to visit some of the botanical gardens with large succulent collections, such as the Huntington, the LA Arboretum, or San Diego Botanical. Drip irrigation will be most effective for your garden design, regardless of the plants chosen. Install the irrigation along with your hardscape to avoid trying to retro-fit under poured concrete.

It looks like any number of neighborhoods in California cities from that era - great looking place. If this were my place, I'd probably use anigozanthos - yellow or green flowered varieties and underplant with aeonium 'sunburst' and/or echeveria 'cante' or dudleya pulverulenta. I would stay away from spiny succulents like aloe ferox since the space is so confined, you're bound to brush up against it. If you do go with a tree aloe, sabaea, thraskii, alooides and speciosa come to mind - those are pretty user-friendly. As far as trees go, perhaps strelitzia nicolai would fit the bill, and could be kept in tight spaces like that. Dodondaea viscosa purpurea could be used as a tall screen in tight spaces like that, as could Leucodendron species like L. eucalyptifolium, discolor, or any number of colorful varieties. Leucadendron argenteum makes a wonderful tree and the color is spectacular in person. Agave attenuata is overused sometimes, but looks great if properly placed. Here are some pictures I pulled off of a quick Houzz search.

Good luck, show us what you end up going with!

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Here are a couple of other ideas. Depending on where you are gardening, you might be able to grow a small palm to give you a bit of height. Dypsis onilahensis, dypsis baronii and chamaeodorea plumosa are wonderful tucked into a corner.